As a rule, your boss can order you to work overtime if there is an explicit overtime regulation in your employment contract. In exceptional cases, however, it may also be possible for your employer to order you to work overtime even if there is no overtime provision in your employment contract and you have to do so. This is the case, for example, in unforeseeable emergency situations for the employer in order to avert short-term dangers for the company or if the existence of the company is threatened.