The answer to this question is nuanced. It is yes, but in certain cases and with certain limits. Employees' pay is indeed protected. The law determines in a restrictive manner the deductions that, alone, can or must be made by the employer from the remuneration of his workers. Five types of deductions are possible without the worker's authorization.
First of all, it goes without saying that the employer must make the deductions provided for by the tax legislation (withholding tax on earned income), the social security legislation (social security contributions) and in application of special or collective agreements on supplementary benefits (personal group insurance contribution, share of meal vouchers, etc.). The employer may also deduct the amount of fines imposed in application of the work regulations. The employer must indicate the breaches sanctioned, the amount and the destination of the fines. Please note: the total amount of fines imposed per day may not exceed 20% of the daily remuneration.
Similarly, the employer may levy indemnities and damages against the employee's liability. Its civil liability may be engaged if the damage caused is the result of fraud (intentional fault, for example: misleading a customer about the value of goods), gross negligence (for example: abandoning a vehicle containing perishable goods) or a light fault of a usual nature (repeated accounting errors, successive cash shortages, errors and negligence in the development of computer programs).
Finally, the employer may make a deduction to recover a cash advance granted by himself from remuneration not yet earned (salary advance or execution of a loan contract). It may also provide a guarantee to ensure the performance of obligations, for example in the case of the handing over of goods to the employee.
With the exception of the statutory tax and social security deductions referred to in point one, all deductions are calculated on cash remuneration only and on pocket wages, after deduction of tax and social security deductions. Total deductions may not exceed 20% of the net cash remuneration due for each pay period.
This 20% limit may be exceeded if the employee has acted with fraud (tortious bad faith, willful misconduct), if he voluntarily terminates his contract before the compensation and damages for which he is liable have been paid, or if he simply agrees to a higher amount.
Apart from the cases cited ("internal" fine, proven fault, advance on salary, deposit), no deductions are authorised without the employee's agreement. If the employer wants to recover money, he must use the ordinary legal procedures, including the use of a bailiff if necessary.
When deductions are to be made for a relatively long period of time, it is preferable to set out the agreement in writing in an agreement signed by the employee.