29 CFR 778.101: Maximum nonovertime hours.

As a general standard, section 7(a) of the Act provides 40 hours as the maximum number that an employee subject to its provisions may work for an employer in any workweek without receiving additional compensation at not less than the statutory rate for overtime. Hours worked in excess of the statutory maximum in any workweek are overtime hours under the statute; a workweek no longer than the prescribed maximum is a nonovertime workweek under the Act, to which the pay requirements of section 6 (minimum wage and equal pay) but not those of section 7(a) are applicable.