About 6-8 months ago the owner of my company decided to stop paying overtime. We have aproximately 50 employees, only 10-12 are comsidered full time. Only one person (not me) is on salary, the rest are hourly. I have tried to stay at only 40 hours a week, there is no incentive for staying any longer.

Yesterday my boss came to me and said that I would have to start putting in more time. As in another 8 hour day. Can they force me to work manditory overtime if they are not going to pay me for it? If I challenge them what can their recourse be? ie-should I start looking for a new job?!?

Yes, they can require you to work mandatory overtime. However, if you are a non-exempt employee, you must be paid for it. They can fire you for refusing the overtime. They cannot fire you for complaining to the DOL about unpaid wages.

How do you determine if you are exempt or non-exempt? Is there an exact formula?

If you are being paid hourly, you are most likely a nonexempt employee, unless you qualify under the Computer Professional exemption.
http://www.dol.gov/esa/regs/compliance/whd/fairpay/fs17e_computer.htm

What exactly are your job duties?

I work for a gym. I do a lot of "back office" work. I talk to members having problems with their accounts. I am also in charge of the front desk, ie- hiring and firing, training. Obvioulsy our accounts are on a computer system, but I am in no way a trained computer professional!

Do you actually hire and fire people? Do you make the decisions? Or do you just process the paperwork? Do you manage at least 2 others? Do you make important business decisions on your own? Did you also check out the Executive and Administrative exemption criteria?
http://www.dol.gov/esa/regs/compliance/whd/fairpay/fs17a_overview.htm

See, here's the issue. If your job duties qualify you for the exemption, the employer MAY treat you as exempt, meaning (in your specific case), a weekly salary of at least $455, overtime pay is not required, and there are specific restrictions on when your weekly salary can be docked. However, they do not HAVE to treat you as exempt if they don't want to.

If they choose to treat you as a nonexempt employee, then you must be paid overtime.

Thank you so much for your help!

I am considered management in the gym, but I do not directly hire and fire people. I can make recomendations. I am definately hourly, and definately make less the the minimum of 455 a week.

I will be pursuing this with the DOL. Again thank you for your time and help!