29 CFR § 778.325 - Effect on salary covering more than 40 hours' pay.
The same reasoning applies to salary covering straight time pay for a longer workweek. If an employee whose maximum hours standard is 40 hours was hired at a fixed salary of $275 for 55 hours of work, he was entitled to a statutory overtime premium for the 15 hours in excess of 40 at the rate of $2.50 per hour (half-time) in addition to his salary, and to statutory overtime pay of $7.50 per hour (time and one-half) for any hours worked in excess of 55. If the scheduled workweek is later reduced to 50 hours, with the understanding between the parties that the salary will be paid as the employee's nonovertime compensation for each workweek of 55 hours or less, his regular rate in any overtime week of 55 hours or less is determined by dividing the salary by the number of hours worked to earn it in that particular week, and additional half-time, based on that rate, is due for each hour in excess of 40. In weeks of 55 hours or more, his regular rate remains $5 per hour and he is due, in addition to his salary, extra compensation of $2.50 for each hour over 40 but not over 55 and full time and one-half, or $7.50, for each hour worked in excess of 55. If, however, the understanding of the parties is that the salary now covers a fixed workweek of 50 hours, his regular rate is $5.50 per hour in all weeks. This assumes that when an employee works less than 50 hours in a particular week, deductions are made at a rate of $5.50 per hour for the hours not worked.