I am a salaried, exempt supervisor and expected to work unlimited hours. Is this legal to require me to complete without additional pay?

I'm assuming your job is properly classified as "exempt" under both federal and state minimum wage and maximum hours laws since you really do not provide sufficient information for me to evaluate your classification status.  IF you indeed qualify as "exempt" under the law, you can be required to work as many hours as needed to do the job without receiving additional pay.  Only employees who are "hourly" or "non-exempt" are entitled to overtime pay after they have actively worked 40 hours in a workweek.  An employee who is "exempt" is "exempt" from the requirement that the employer pay them overtime.