Article R1237-13 of the French Labour Code
The employer who finds that the employee has abandoned his post and intends to invoke the presumption of resignation provided for in article L. 1237-1-1 shall give him formal notice, by registered letter or by letter delivered personally against receipt, to justify his absence and to return to his post. In the event that the employee intends to invoke a legitimate reason from the employer such as to preclude a…