I was employed at a personally owned small mini-mart (gas station) as a labor. Duties was stocking shelves, cashier, sweeping-mopping floors, etc. I was told I could not be paid overtime under mo. law because the did not make enough money yearly. is there an exemption keeping them from paying me overtime? I was receiving a hourly wage of $6.00 per hour.

Employers who make under $500,000 yearly in total, are exempt from the FLSA.

It's possible however, that even so, they still could be regulated under Missouri law. Unfortunately, the MO Dept of Labor web site is down at the moment. I'll try to check on that again later.