Good day, 

In terms of the 13th Salary, it depends on what is specifically mentioned in the employment contract. 

It also depends on industry and if there is a collective agreement in place forcing an employer to payout a 13th salary that is not based on performance or subject to operational standards. If the employment contract states that all employees will receive an additional salary on perhaps their birthdays then an employee may proceed to claim this from its employer. 

In any other circumstance apart from the above mentioned,  the employer cannot be forced to payout  a 13th Salary. In most cases the 13th Salary is seen as an incentive and therefore subject to terms and conditions set out by the employer. 

Kind Regards, 

LP