This is a very tricky problem, subject to complex rules under the Fair Labor Standards Act and many state laws.
Great caution is advised.
Someone from Wisconsin asked this question in January 1995. The idea is to call up the spectre in bosses' minds of employees who are secretly documenting unfair requests over years and years, then suddenly showing up with a federal order for back compensation in the thousands of dollars. Large organizations can be so paranoid about this prospect that they punish supervisors who even allow employees to deviate from the standard work hours even when everyone involved is committed to achieving some short-term goal and totally innocent of the above sorts of thoughts. If you have a real problem along these lines, I suggest contacting the Wage and Hour branch of the US Department of Labor and getting the published info they have about it, then creating a nonconfrontational way of bringing these rules to everyone's attention. Their roots are in genuine forms of oppression and exploitation.