The requirement that overtime must be paid after 40 hours a week cannot be waived by agreement between the employer and employees. Similarly, an agreement that only eight hours a day or only 40 hours a week will be counted as working time will clearly fail. An announcement by the employer that no overtime work will be permitted, or that overtime work will not be paid for unless authorized in advance, also will not impair the employee’s right to compensation for the overtime work that the employer suffers or permits (has knowledge of).