In German labor law, a benefit an employer repeats regularly can become an entitlement. This is called betriebliche Übung, company practice. The classic case is a Christmas bonus. If an employer pays it three years in a row without stating in writing that it is voluntary, the employee can claim it in the fourth year. The employer cannot simply withdraw a right created this way. He must give formal notice of changed terms of employment, an Änderungskündigung.