The article presents an analysis of employees’ obligation to be sober in the context of legal possibilities of running preventive sobriety tests on employees. It thoroughly discusses the Supreme Court judgment policy on employees’ obligation to be sober in the workplace and legal consequences of their failure to fulfil this duty. The article also conducts a critical analysis of the opinion that an employer can carry out preventive checks only based on an employee’s consent expressed on his/her own initiative. The author proves that a contrary thesis is right and that, in case of some jobs, such as drivers or persons working at height, an employer is obliged to do preventive tests for employees’ sobriety and employees are obliged to take such tests. At the same time, employees’ consent to process data concerning the state of their sobriety is not required.