Undeclared work is not only a legislative violation, but also a loss of rights and guarantees for employees.
If you work without employment contract, you cannot count on guaranteed paid holidays, sick leave or compensation in case of an accident. You also do not have protection against arbitrary dismissal, salary reduction and work overload. Do not be fooled by employers who offer you to work without employment contract, with a salary "in the envelope" or under the civil law contracts.
Demand registration of labor relations according to the law!
Declared work is your right and your benefit!