The subject of the article. Traditionally, it is used to assess the legality of actions taken by participants in civil matters. Nevertheless, although the concept of "vice of will" is deeply developed in civil law, its application to labour relations remains ambiguous due to the specific socio-economic nature of labour and the special legal mechanisms designed to protect the interests of employees.The purpose of the study. Development of a special approach to the use in labor law of categories borrowed from civil law related to the vice of the will, as well as special rules for identifying defects in the will of the employee.Methods. Empirical methods of comparison, description, interpretation as well as formal legal method.Conclusions. The admissibility of applying analogies and uncontrolled use of terms from civil law in labour dispute judicial practice are refuted, and a set of special rules is proposed for consideration in cases where it is necessary to establish defects in the will of an employee. Among these rules is the need to maintain a balance of interests between the parties to labour relations as a defining principle in adjudication on the matter of establishing the will of the parties. The freedom of defining the legal terms of any agreement between an employee and an employer, in the absence of legal restrictions, should in any case be limited by the inadmissibility of attributing objective risks associated with the employer's business activities to the employee. At the same time, the application of "contra proferentem" interpretation to disputed terms, with the burden of proof placed on the employer to demonstrate the employee's voluntary consent to such terms, is permissible only if the employee provides evidence of the clearly and obviously onerous nature of these conditions. The priority of the actual will of the parties and the refusal to recognize the legal significance of the expression of will is possible in any case in the absence of signs of bad faith referring to the depravity of the party, declared within the time limits prescribed by law to appeal to the court, provided that such a decision will not entail violations of the requirements of the law or other legal act or infringe on public interests. If circumstances of vice of will are identified, arising from lawful managerial decisions of the employer or the likelihood of such decisions being made regarding the employee, the legal consequences are inapplicable. The assessment of the appropriateness of the employer's lawful managerial decisions should not be subject to judicial review.