This is perfectly legal. The law does not restrict the number of hours an employee may work, but merely requires that if the employee is hourly, he or she be paid for all hours worked--and if not exempt from ovetime, that he or she be paid overtime for hours over 40 in a week.Employers have considerable discretion in setting the terms and conditions of employment, including hours worked, and can essentially require anything not itself illegal. Since it is not illegal to have employees work 50 (or more) hours a week, an employer may make this a condition of employment or a term in an employment contract, subject only to the obligations regarding hourly pay and overtime pay discussed above.