1- WHAT IS OVERWORK?
If an employee exceeds weekly working hour which is 45 hours as stated in Labor Law, he/she will be regarded that he/she is overworking.

Longtime working: if weekly working hours are determined as less than 45 hours in labor agreement and employee exceeds that determined weekly working hour, it will be considered as longtime working.

2- HOW MANY HOURS CAN AN EMPLOYEE OVERWORK?
In article 41 of the Labor Law numbered 4857, total amount of longtime working cannot be more than 270 hours in a year.

Source: Labor Law