Can you pay an invoice without protest and later dispute unilaterally changed pricing terms?

Paying an invoice without reservation generally implies acceptance of that invoice and its terms and conditions. When a trading partner unilaterally changes agreed prices or discounts, timely protest is important; those who remain silent and pay tacitly agree to the new terms. Below, we discuss a ruling of the Antwerp Court of Appeal dated Jan. 8, 2025 that highlights this strict legal reality within B2B relationships.

The facts

Two companies, S. BV (a bakery) and SAS BV (operator of bread stores and vending machines), entered into an oral agreement in July 2022. S. BV would supply uncut bread at an agreed price, on which a standard discount of 35% was granted.

In May 2022, S. BV suddenly billed a higher bread price and unilaterally applied a lower discount of 25%. SAS BV formally protested the higher bread price, after which S. BV sent a credit memo to neutralize the price increase, but this retained the reduced discount of 25%. SAS BV paid the invoice with the lower discount, as well as subsequent invoices, without any further reservation.

At the end of June 2022, the cooperation was terminated. S. BV believed that SAS BV had terminated the agreement unilaterally and without notice, and demanded hefty damages for loss of income. However, SAS BV disagreed: it argued that S. BV's unilateral reduction of the discount was at the root of the breach, and that the cooperation was finally terminated by mutual agreement. S. BV argued to the contrary that SAS BV had indeed agreed to 25%'s new, lower discount simply because it had paid the invoices without reservation.

The decision

The Antwerp Court of Appeal ruled that payment of an invoice implies acceptance of that invoice. Moreover, a lack of protest against an invoice (or in this case, a credit note) also results in tacit acceptance.

Although the discount granted was an essential part of the agreement, the court found that S. BV had unilaterally modified it. However, because SAS BV paid three invoices and the credit memo in which this reduced discount was applied without any reservation and did not protest, the court ruled that there was indeed an acceptance of the modified conditions.

In addition, the court rejected the claim for damages for breach of contract. The lack of protest against the termination and the content of Messenger messages from the director of S. BV showed that the agreement had been terminated by mutual agreement on June 28, 2022.

Legal analysis and interpretation

S. BV sought in these proceedings to justify its initial, unilateral price increase by invoking the “complementary effect of good faith.” To do so, it referred to the standard of conduct in article 1134, paragraph 3 of the old Civil Code, which states that contracts must be executed in good faith, implying loyal cooperation and consideration of each other's interests. The court rejected this reasoning, stating that SAS BV's refusal to simply agree to a unilateral increase was not at all inconsistent with the conduct of a reasonable contractor. After all, commercial parties do not pursue a common goal in a mere supply agreement, but rather represent their own financial interests.

Incidentally, the Parties in this case confuse two legal concepts: the supplementary effect of a contract on the one hand, and the unilateral modification of a contract on the other. The complementary effect (enshrined in Article 1135 old Civil Code, and the current Article 5.71 Civil Code) serves only to fill in gaps in an agreement based on fairness. It is not a license to ignore existing agreements. What S. BV on the other hand did was to unilaterally modify an already made agreement (which violates article 1134, second paragraph old Civil Code. Under the new law of obligations, such unilateral modification (the so-called party decision via Article 5.70 Civil Code) is only possible if the contract expressly permits this in advance.

What this specifically means

This case is a warning to every company. Within business law, an accepted or unprotested invoice constitutes ironclad evidence, in accordance with Article 8.11 of the Civil Code.

• Protest in a timely manner: Do you disagree with a lower discount, a price increase or other unilaterally changed conditions? Respond immediately with a reasoned, written protest.
• Don't pay indiscriminately: Pay only the undisputed portion. Anyone who pays an invoice with changed commercial terms in full and without reservation legally agrees to the change.
• Be mindful of your informal communications: The case law perfectly accepts exchanged instant messages (such as via Messenger or WhatsApp) as evidence, for example, for the amicable termination of a business relationship.

FAQ (frequently asked questions)

How do I protest an invoice correctly?
Always do this in writing and preferably through a provable channel (registered mail or e-mail with acknowledgement of receipt). Clearly state the invoice number and motivate specifically which unilaterally changed conditions (such as a price or discount) you reject.

Can my supplier simply reduce or eliminate its discounts?
An awarded discount is often an essential component of your contract. A unilateral change is allowed only if your contract or the applicable general conditions expressly provide for it. Without that clause, it cannot be done unless you yourself tacitly agree by paying the invoice without protest.

Are WhatsApp or Messenger messages legally valid as evidence?
Yes. In business-to-business (B2B) disputes, freedom of evidence applies. Belgian courts regularly accept electronic chat messages as full proof of mutual agreements or terminations.

Conclusion

Failure to protest invoices or protesting them late can deprive you in Belgium of the opportunity to challenge unilateral contract changes, such as price increases or reduced discounts. Once you pay without reservation, you agree.