The reduction of working time must be regarded as a substantial change to the employment contract.
Thus, the fact that an employer notifies to an employee a reduction of his working time, for example from 40 to 32 hours per week, is to be regarded as an essential change to the employment contract detrimental to the employee.
The view has nevertheless been taken in the case law, in a case of an increase of working time, that the change to the working time in the contract of an employee without her consent, namely from part-time to full-time, and therefore involving an increase of wages, is a unilateral change to a substantial clause of the contract in favour of the employee, and in any such case Article L. 121-7 of the Labour Code is not applicable.
In the event of litigation between the parties, it will be incumbent on the employment courts to determine whether the change of working time is to be regarded as a substantial or non-substantial change to the employment contract.