Labour law, embodies a number of mandatory provisions in order to protect employees who are in a weaker position vis-à-vis employers. Moreover, Article 420 of the Code of Obligation no. 6098 has forbidden any act having effect of withdrawal of employees from their rights. Thus, validity of settlement agreement, termination of the employment contract by mutual agreement, release of debt and agreements acted at the end of the process of mediation -which has become more and more important as it is stipulated as mandatory with the Code no. 7036- constitute an issue of debate entangled with one another. This study examines whether employees could renounce their rights ensured by mandatory provisions, and explores the conditions of validity for termination by mutual agreement and settlement agreement in labour disputes, and agreements acted at the end of the process of mediation.