Is it illegal for an employer to ask an hourly employee to work more than 16 hours on a shift?

In the absence of a contract, including a union contract, there is generally no limit to the number of hours an employer can ask or required an employee to work in a work day or work week.  However, when an employee's hours exceed 40 in a single work week, most employers are required to pay overtime which is 1.5 times the employee's usual hourly rate.  There are execeptions to this overtime pay requirment for managers, owners, professionals, office administrators and others exempt from the overtime requirements of the FLSA.