The Supreme Court on the written form of contract amendments

In its judgment of 27 August 2025, Case No. 23 Cdo 2565/2024, the Supreme Court of the Czech Republic addressed the question of the validity of an amendment to a work contract made in a form other than the originally agreed form. 

The case considered by the Supreme Court concerned a work contract between a client and a contractor for construction work. It was agreed in the contract that the work was to be completed within 120 calendar days of the handover of the site, with the handover of the site to be confirmed by a written report. Amendments to the contract were to be made only by written amendments, otherwise they are ineffective. However, the client later emailed the contractor and asked him to start the work immediately, without a site handover report being drawn up. The contractor started the work and both parties effectively continued the contractual relationship without following the formal procedure.

After the deadline for completion of the work, the client withdrew from the contract on the grounds that the work had not been completed on time. The lower courts, however, held the withdrawal to be invalid because, according to them, the time limit for completion had never begun to run due to the absence of a handover report. The Supreme Court disagreed with this interpretation. It pointed out that the real intent of the parties and their subsequent conduct needed to be examined. If the contractor commenced work and the client accepted this, there may have been an implied agreement to amend the contract (including waiving the requirement for written form).

The Supreme Court has confirmed that if a certain form is required only by agreement of the parties (e.g., a written form for amendments to a contract), the parties may jointly modify or omit it after the fact, unless the contractual provisions preclude it. A legal act that does not comply with the agreed form is invalid, and the invalidity can be remedied subsequently, e.g. by an amendment in the required form. 

Further, the court emphasized that subsequent conduct of the parties is relevant for the agreement to waive the agreed form. By the actual handover of the construction site and the contractor’s subsequent commencement of work with the client’s knowledge, both parties expressed their will to continue the contractual relationship, even without the agreed written form.

It follows from the above decision that not only the content of the contract but also the subsequent conduct of the parties is of legal significance. It is therefore essential that contractual practice is consistent with the stated formal requirements if these requirements are to be effectively enforceable.