I believe there is no law if you cant finance legal action. Nowadays we have tons of flexible and temporary contracts. These people have just about the right to do as they are told. If you have a contract for a fixed number of hours and unlimited duration that doesn't mean the employer has to stick to the rules. It really doesn't matter what laws or contracts there are. In some companies (hard to tell how many) it's a game of looking what they can get away with. For a union there is prestige in court over [say] a 30 euro pay cut or a few unpaid hours.