Labour contract is a contract which consists on, performing duties, wage and dependency. From those elements, performing duties is as a debt embodied on the labour. The employee must perform his / her duties as required by the nature of the work as stipulated in the contract and by his / her characteristics. Otherwise, there will be a violation of the contract. In case the employee fails to fulfil his / her duty as required, there is a situation of incomplete performance or non-performance of his / her duties. The employer can resort to various sanctions if the employee breaches his debt. The most severe of these sanctions and therefore the most important in terms of labour law is the termination of the employee’s labour contract. It is possible to speak of termination for a valid reason if the employee fails to fulfil his duty and termination for a justifiable reason if the employee’s duty of debt is not fulfilled at all. Although the employer’s right to termination for a rightful reason has been regulated in the Labour Law No. 4857, the rightful reasons are not limited. In this context, it was necessary to discuss the situation in which the worker violated his duty to work and whether this could be considered as a reason for termination without summary. In our study, we will evaluate the situation in which the employer can exercise the right of termination in case the employee has never fulfilled his / her debt. In this context, firstly, the scope of the obligation of performing the duties of the labour and in which case the working debt has never been fulfilled; then, the right of termination of the employer for a good cause and the moment of birth and the circumstances under which this right can be exercised will be discussed.