Guide
Does the CISG Govern Your Purchase of Machined Parts from a Vietnamese Supplier?
The CISG is the United Nations Convention on Contracts for the International Sale of Goods, a treaty that applies by default to a sale of goods between businesses whose places of business are in different Contracting States. The short answer: for a U.S. buyer and a supplier with its place of business in Vietnam, both countries are Contracting States, so the CISG normally governs the sale unless the contract excludes it. Decide on purpose whether to keep it, exclude it or modify it, because silence means it applies.
By Saola Manufacturing engineering team · Published · Updated
General information, not legal advice. The CISG and the UCC are legal texts that courts interpret; have counsel review your supply agreement and the choice of governing law.
This guide is for procurement or legal staff at a U.S. company writing or reviewing a purchase contract for machined parts with a Vietnamese supplier. Many buyers do not realize the Convention applies unless it is excluded. The guide covers when it applies, what it changes compared with the U.S. Uniform Commercial Code (UCC), the options for governing law, and what to write into the agreement. It is written for engineers and buyers, so it describes the rules in plain terms and leaves conclusions to counsel.
On this page
When does the CISG apply to a purchase from Vietnam?
It applies to a contract of sale of goods between parties whose places of business are in different States when those States are Contracting States, and it applies automatically unless the parties exclude it. The United States and Viet Nam are both Contracting States.
Article 1(1)(a) sets the rule: the Convention applies to contracts of sale of goods between parties whose places of business are in different States when the States are Contracting States. The nationality of the parties and the civil or commercial character of the contract are not considered (CISG text, UNCITRAL, 2010). What counts is where each party has its place of business, not where the parts are made or shipped from. A U.S. buyer contracting with a Vietnamese company is the case the rule describes; a U.S. buyer contracting with a U.S. distributor that imports the parts is not, because both places of business are in the same State.
The UNCITRAL status page lists the United States as having ratified on 11 December 1986, with entry into force on 1 January 1988, and Viet Nam as having acceded on 18 December 2015, with entry into force on 1 January 2017. The United States declared that it would not be bound by Article 1(1)(b), which does not matter for a direct sale to Vietnam because Article 1(1)(a) already covers it (UNCITRAL status table). Viet Nam made a separate declaration under Articles 12 and 96, discussed below. On the U.S. side, the Department of State published notice of the ratification with the official English text of the Convention in the Federal Register (52 FR 6262, March 2, 1987).
Do custom machined parts count as a sale of goods?
Yes in most cases: Article 3(1) treats a contract to supply goods that are to be manufactured as a sale, unless the buyer supplies a substantial part of the materials. A contract where the preponderant part of the supplier's obligations is labor or services is outside the Convention.
Machined parts made to your drawing are goods to be manufactured, so a supply agreement for them generally falls within Article 3(1). Two situations can change that. If you supply a substantial part of the material yourself, for example consigned bar stock or castings you buy and send for machining, the exemption in Article 3(1) is in play, and so is Article 3(2), which excludes contracts where the preponderant part of the supplier's obligations is the supply of labor or other services. A pure machining-service arrangement on your material sits closer to that line. Ask counsel how the facts of your arrangement are likely to be read before relying on either answer.
The Convention also lists sales it does not cover, including goods bought for personal, family or household use, auctions, and sales of ships and aircraft (Article 2). A production purchase of metal components by a business does not usually fit any of those exclusions. Article 4 adds that the Convention governs formation and the rights and obligations of buyer and seller; it does not decide the validity of the contract or of any of its provisions, nor the effect of the contract on property in the goods. That is why the domestic law you choose still matters even when the Convention applies.
What does the CISG change compared with the UCC?
It changes the default rules on replies with different terms, modification, notice of defects and interpretation. Most of the differences matter when a dispute is already under way, so check them before you sign, not after.
The table compares the points that most often matter in a machined-parts relationship. It states the default rule in each text and is not a prediction of how a court would decide your case.
| Topic | CISG default | UCC Article 2 default |
|---|---|---|
| Form of the contract | No writing required (Art. 11), but not where a party's place of business is in a State that made an Art. 96 declaration, which includes Viet Nam (Art. 12) | Writing rules under section 2-201, not reviewed in this guide; check with counsel |
| Reply with different terms | A reply that adds or changes terms is a counter-offer (Art. 19(1)); minor changes can still be an acceptance unless the offeror objects promptly (Art. 19(2)); changes to price, quality, liability or dispute settlement are material (Art. 19(3)) | A definite acceptance can form a contract despite different terms (2-207(1)); between merchants additional terms join unless the offer limits acceptance, they materially alter it, or the other party objects (2-207(2)) |
| Modification | May be modified by mere agreement (Art. 29(1)); a clause requiring writing for changes is respected, subject to reliance (Art. 29(2)) | Needs no consideration (2-209(1)); a signed-writing clause generally controls (2-209(2)) |
| Notice of defects | Reasonable time after discovery, and no later than two years from handover unless a contract guarantee period is longer (Art. 39) | Reasonable time after discovery or the buyer is barred from any remedy (2-607(3)(a)) |
| Time to bring a claim | Not in the CISG itself; the explanatory note says a companion Limitation Convention covers it, so confirm with counsel which rules apply | Four years from accrual, reducible by agreement to not less than one year (2-725) |
| Excused failure | Impediment beyond control that could not reasonably be taken into account (Art. 79) | Separate Code provisions, not reviewed in this guide |
What does Vietnam's writing declaration mean for your orders?
Under Articles 12 and 96, the Convention's rules that allow an offer, acceptance, modification or termination in a form other than writing do not apply where a party has its place of business in Viet Nam. In practice, put orders, acceptances and changes in writing.
The UNCITRAL status table records that Viet Nam made this declaration (UNCITRAL status table). Article 12 states that the parties may not derogate from or vary its effect, so a clause in your agreement cannot switch the writing requirement off.
The CISG text does not say whether an email or a messaging-app confirmation counts as writing for this purpose; the UNCITRAL explanatory note points to a separate 2005 Electronic Communications Convention on electronic communications in international contracts, and whether it applies between the two countries is a question for counsel. Do not rely on a verbal change to a drawing, a chat agreement on a delivery date or a handshake on a price. Ask counsel what form your confirmations should take, then keep to it: written orders, written acceptances and written amendments, signed or sent in the way the agreement specifies.
How do you exclude the CISG or change how it works?
Article 6 lets the parties exclude the Convention or vary the effect of any of its provisions, subject to Article 12. There are three plain options: keep it, exclude it and choose a domestic law, or keep it and write the specific rules you need.
Keep it. You accept the default rules in the table, including the Article 39 notice rules and the Article 19 treatment of replies. This works if your contracts are signed, short and clear, and your counsel is comfortable with the Convention.
Exclude it. The agreement states that the Convention does not apply and names the governing law, for example the law of a U.S. state, so the UCC would apply. Be precise about the wording: the Convention is itself part of the law of a Contracting State, so a clause that only selects a state's law may not accomplish an exclusion. This is a drafting question to put to counsel, not an assumption to make.
Keep it and vary it. Article 6 allows parties to derogate from or vary the effect of its provisions. Write the rules you care about into the agreement: a defined inspection window, a defined claim period, who bears the cost of nonconforming lots, how changes are made, and what counts as an impediment. The contract then controls, and the Convention fills gaps. Whichever you choose, say so in a governing-law clause, because silence leaves the default in place.
Which option fits a recurring production program?
For a recurring program, one signed master supply agreement that states the governing law, the writing rules and the key quality terms is more useful than a choice between the two legal systems. The agreement does more work than the default.
A program of 10,000 to 20,000 parts a year runs on purchase orders over many months. Under the Convention, a purchase order reply that changes price, quality, liability or dispute settlement is treated as materially altering the offer (Article 19(3)), so conflicting forms become a counter-offer, and the exchange of forms can leave terms unsettled. A master agreement that every purchase order refers to removes most of that. How U.S. law handles the same exchange of forms is covered in the guide on purchase order terms versus supplier quote terms.
Align the other documents with the choice. The conformity standard in Article 35, under which goods must fit their ordinary purposes, any particular purpose made known to the seller, and the qualities of any sample or model the seller held out, pairs naturally with a written quality requirement and an approved sample (see golden samples and limit samples and the supplier quality agreement guide). Confidentiality is a separate document; the choice between an NDA and an NNN is in the NNN versus NDA guide.
What should you do before the first purchase order?
Ask counsel to settle the governing-law clause, write the writing and notice rules into a master agreement, and send the supplier your drawings and quality requirements with the RFQ so the technical terms are not left to default rules.
Saola is the brand of a Ho Chi Minh City company, so a sale to a U.S. buyer is the case this guide describes. Contract terms are agreed project by project and are for your counsel to review. To start on the technical side, send the drawing and the quality requirements through the quote page; the parts are made by CNC turning and CNC milling at the lead plant.
Frequently asked
Does the CISG still apply if my purchase order says it is governed by the law of a U.S. state?
Possibly. Article 6 allows exclusion, but whether a clause that names only a state's law does that is a drafting question. If you want it excluded, have counsel write the exclusion expressly.
Does the CISG apply to parts I design and the supplier makes?
Generally yes. Article 3(1) treats a contract to supply goods to be manufactured as a sale, unless the buyer supplies a substantial part of the materials. Consigned material changes the analysis, so raise it with counsel.
Are verbal orders to a Vietnamese supplier valid?
Under Articles 12 and 96, the rules allowing a non-written offer, acceptance or modification do not apply where a party has its place of business in Viet Nam. Put orders and changes in writing and ask counsel about email.
Is two years the warranty period?
No. Article 39(2) is an outer limit for giving notice of a lack of conformity, and it yields to a longer contractual guarantee period. Set the warranty period you want in the agreement.
Can I exclude only part of the CISG?
Yes. Article 6 lets the parties derogate from or vary the effect of any provision, subject to Article 12. Write the specific rules you want into the agreement.
Sources
- United Nations Convention on Contracts for the International Sale of Goods (full text), United Nations Commission on International Trade Law, New York, 2010
- Status: United Nations Convention on Contracts for the International Sale of Goods (Vienna, 1980), UNCITRAL, accessed 2026
- U.S. Ratification of 1980 United Nations Convention on Contracts for the International Sale of Goods: Official English Text, Department of State Public Notice 1004, Federal Register Vol. 52, No. 40, p. 6262, March 2, 1987
- United Nations Convention on Contracts for the International Sale of Goods (1980) (CISG), UNCITRAL, accessed 2026
- UCC 2-207, Additional Terms in Acceptance or Confirmation, Legal Information Institute, Cornell Law School, accessed 2026
- UCC 2-209, Modification, Rescission and Waiver, Legal Information Institute, Cornell Law School, accessed 2026
- UCC 2-607, Effect of Acceptance; Notice of Breach, Legal Information Institute, Cornell Law School, accessed 2026
- UCC 2-725, Statute of Limitations in Contracts for Sale, Legal Information Institute, Cornell Law School, accessed 2026