The Labour Code does not regulate the issue of defects of declaration of intent. In this respect, the provisions of the Civil Code to labour relations are applied under art. 300 of the Labour Code. The auxiliary application of the rules of civil law is therefore possible only in the case of loopholes in labour laws. In the case of the deception of the declaration of intent in labour law, the loophole is not obvious. To confirm its existence, the limits of its application to employment relationships of the institution terminating the employment relationship without notice (under art. 52 of the Labour Code), and the legal concept of the deception of declaration of intent regulated in art. 86 of the Civil Code, in conjunction with art. 300 of the Labour Code, need to be considered. for this purpose, the author distinguishes the effects of fraudulent declarations of intent at the stage of establishing and terminating the employment relationship as well as during its term. She analyses the reasons for avoiding the effects of declarations of intent made under the influence of deception of the other party of the employment relationship, or a third party. She considers the importance of silence and lies at the stages of the establishment, the duration and the termination of employment for the application of art. 86 of the Civil Code in conjunction with Art. 300 of the Labour Code to the employment relationship, and the consequences of avoiding the effects of a declaration of intent made under deception, as well as in the situation when work has been already exercised.