Can an employer not pay you for time worked because of a failed drug screen?

I got a job with a community action group and was not aware of the drug screen. After I found out, I felt that I would pass since it had been quite a while since my last use so I took the test and hoped for the best. It took 5 days for the results to come back to the employer and I worked for those 5 days for 7 hours a day. I didn't pass the drug screen so they terminated my position. I brought back all the gear they had requested and signed paperwork that the crew leader said would get my paycheck to me without me having to come by and pick it up. I waited 3 weeks and never got a paycheck. I started calling the crew leader and she just ignored my messages and wouldn't call me back. I finally e-mailed the director of the program and she informed me that I would not get paid for the hours worked because of the failed drug screen. Can this really be allowed?