By Prakhar Rai, Founder, My Legal Pal. Advocate, Bar Council of India. LL.B, NLSIU Bangalore. Master of Business Laws.
Quick answer: If your purchase order says one thing and your signed contract says another, a master agreement that says it overrides purchase orders usually wins. If there is no master agreement, the answer depends on the country. England looks at who sent the last document the other side accepted, which is the “last shot”. The US for sales of goods, Germany and France tend to knock out the clauses that conflict and fill the gap with default law. India treats a reply with different terms as a counter-offer.
Key takeaways
- A purchase order (PO) is usually an offer. An order acknowledgment with different terms may be a counter-offer, not an acceptance.
- The same exchange of forms can end three ways: last shot, knock-out, or counter-offer.
- The cure is drafting. An order of precedence clause in the master agreement, and POs that refer back to it, fix most of the risk.
- Object in writing to terms you can’t accept, before you perform. Conduct can bind you.
- For international sales of goods, the CISG can apply unless you exclude it.
A buyer sends a PO that says “payment in 60 days, unlimited liability for defects”. The seller replies with an order confirmation saying “payment in 30 days, liability capped at the order value”. Goods ship and are accepted. Months later something goes wrong. Whose terms apply?
Companies that negotiate a careful master agreement often forget that every later PO and invoice can carry its own terms. The master agreement only protects you if it says it does.
This guide covers conflicts between standard-form documents. For the master contract itself, see our guide to the master service agreement, and for how a work order sits beneath it, the statement of work.
The “battle of the forms”
Lawyers use the phrase when two parties exchange documents containing their own standard terms and each conflicts with the other. Nobody negotiated the terms. They are on the back of a PO, in a portal, or in an invoice footer. Yet a dispute can turn on them.
Four approaches
| Approach | Idea | Where you find it |
|---|---|---|
| Mirror image and counter-offer | Acceptance must match the offer. A reply with different terms is a counter-offer | India (Contract Act, section 7), English common law, CISG Article 19 baseline |
| Last shot | The last document sent before performance, if not objected to, carries the terms | England (traditional rule) |
| Knock-out | Conflicting clauses cancel out and the law supplies default terms | US (UCC 2-207), Germany, France, UNIDROIT Principles |
| Contract wins | A signed master agreement with a precedence clause overrides later forms | Everywhere, if the clause is well drafted |
Country by country
United States
For the sale of goods, UCC section 2-207 relaxes the mirror image rule. In outline: an acceptance that adds different terms can still form a contract unless it is expressly made conditional on the offeror’s assent to them. Between merchants, additional terms may become part of the contract unless the offer limits acceptance to its terms, the new terms materially alter the deal, or the other side objects. If the parties perform without a clear agreement, section 2-207(3) lets the contract be found in their conduct, and many courts knock out the conflicting terms and use UCC default rules instead. States differ, so this is a guide, not a prediction.
The UCC covers goods. Contracts for services are generally governed by common law offer and acceptance rules, which are stricter.
United Kingdom
English courts apply traditional offer and acceptance rules. In Butler Machine Tool Co. v. Ex-Cell-O Corporation (England) Ltd [1979] 1 WLR 401, the buyer’s order was treated as the controlling offer, and the seller’s acknowledgment as accepting the buyer’s terms. In Tekdata Interconnections Ltd v. Amphenol Ltd [2009] EWCA Civ 1209, the Court of Appeal applied the traditional analysis and the seller’s terms prevailed. In TRW Ltd v. Panasonic Industry Europe GmbH [2021] EWCA Civ 1558, a carefully drafted set of terms that excluded other terms helped the party that had written them. Practical lesson: the party that keeps a clear paper trail and states its terms in each document tends to do better.
Germany
German courts apply the knock-out rule. In the CISG context, the German Federal Court of Justice’s milk powder decision of 9 January 2002 rejected the last shot rule and applied a knock-out approach, according to the CISG case-law database. Under the Civil Code, conflicting standard terms that don’t match cancel each other, and the statutory default rules fill the gap.
France
Article 1119 of the Code civil provides that general conditions bind the other party only if brought to its attention and accepted, and that where each party’s general conditions conflict, the incompatible clauses have no effect. In practice that is a knock-out rule. A CMS guide to French law also notes that the seller’s general terms of sale are the starting point of commercial negotiation under French commercial law.
India
Section 7 of the Contract Act requires acceptance to be absolute and unqualified. An acceptance with a variation is a counter-offer. In Padia Timber Company Pvt. Ltd. v. Board of Trustees of Visakhapatnam Port Trust ((2021) 3 SCC 24), the Supreme Court treated an added condition as leaving the contract incomplete until the offeror agreed. In Saarschmiede GmbH v. Bharat Heavy Electricals Ltd. (Delhi HC, 2019), purchase orders bound the supplier on their terms because it did not object within the stated period. I’d check both reports before citing them.
The CISG and international principles
The UN Convention on Contracts for the International Sale of Goods (CISG) applies to many cross-border sales of goods between parties in contracting states, unless the contract excludes it. Article 19 follows the counter-offer logic: a reply that adds or changes terms is a rejection and a counter-offer, but one that adds non-material terms can still operate as an acceptance unless the offeror objects. In practice, tribunals have used both last shot and knock-out approaches, and the German decision above applied knock-out. The UNIDROIT Principles (Article 2.1.22) favour knock-out. Check whether your contract excludes the CISG and whether your countries are parties.
How to make your terms win
- Put an order of precedence clause in the master agreement. For example: the master agreement prevails over any PO, order confirmation or invoice, and no PO term applies unless signed by both parties.
- Make each PO refer to the master agreement. A PO that says “issued under the MSA dated X” is harder to turn into a separate contract.
- Exclude other terms expressly. A sentence stating that any additional or different terms in a PO, acknowledgment or invoice are rejected, unless agreed in writing, helps.
- Object promptly. If a PO arrives with a clause you can’t accept, reply in writing before you ship.
- Don’t perform on unresolved terms. Conduct can bind you, and in some systems a contract formed by conduct includes only the terms the forms agree on.
- Control the portal. If a procurement portal asks you to tick “I accept the terms”, assume you’re bound.
- Add an entire agreement clause. It should say the master agreement and signed schedules are the whole agreement.
- Choose the governing law deliberately, and say whether the CISG applies.
A sample precedence clause
“In the event of conflict, the following order applies: (1) the Master Agreement; (2) the applicable Statement of Work; (3) any Purchase Order. Any terms in a Purchase Order, order acknowledgment, invoice or similar document that add to or conflict with this Master Agreement are rejected and do not apply unless signed by an authorised representative of both parties.”
Use it as a starting point. Whether it works depends on the governing law, and a lawyer should fit it to your documents.
What goes wrong most often
- No master agreement. Each PO becomes a stand-alone contract.
- Conflicting liability terms. The PO says unlimited, the acknowledgment says capped. See our article on limitation of liability.
- Different indemnity or IP terms. See our guide to the indemnity clause.
- Service levels in one document, remedies in another. Our explanation of the service level agreement shows how they should link.
- Silence read as consent. In many systems, shipping goods after receiving a PO can be treated as acceptance by conduct.
If you want your master agreement and PO templates to fit together, our MSA drafting service and contract review and revision team can align them.
Quick answers
Does a purchase order count as a contract? It’s usually an offer. When the seller accepts it, or performs, a contract can form, and which terms apply depends on the seller’s response and the governing law.
Which wins: the PO or the master agreement? If the master agreement says it prevails and the PO was issued under it, the master agreement generally wins. Without such a clause, the answer turns on the facts and the law.
Are the terms on the back of an invoice binding? Not automatically. They bind only if they became part of the contract, for example by agreement or a consistent course of dealing.
What is the knock-out rule? Where the parties’ forms conflict, the conflicting clauses cancel and default law fills the gap. It is used in the US (for goods), Germany, France and the UNIDROIT Principles.
What is the quickest fix? Add an order of precedence clause to your master agreement and make every PO refer to it.
A note on who we are
My Legal Pal is an international team of contract lawyers with US law experience. We aren’t a US law firm, and we aren’t a local firm in every country mentioned above. This article is general information and not legal advice on your facts. Have a lawyer qualified in the governing jurisdiction check the details before you act.
About the author. Prakhar Rai is an advocate enrolled with the Bar Council of India and the founder of My Legal Pal. He holds an LL.B from NLSIU Bangalore and a Master of Business Laws, and works on contract drafting, review and disputes for founders and businesses across borders. Full profile
