I normally work 8-5 M-F in an office environment for a service company in PA, but I am sometimes required to work on customer equipment at their location. The new management of the company requires office people to work 40 hours/week, or they will take (and pay you for) your vacation hours to make 40. A situation arose that would have given me overtime, except that my employer told me to go home once I reached my 40 hours. My work week was:

Mon - 8 hrs
Tues - 13.25
Wed - 7.75
Thur - 7.75
Fri - 3.25

Can they legally do this and not pay any overtime? Thanks for any response.

Yes, they can legally require you to go home early to avoid paying overtime under the circumstances you describe. While, if you work overtime, they must pay it, nothing in the law requires them to allow you to work overtime if they don't want you to.

Thanks for the reply, I was afraid that was the answer.

Does it make a difference as to whether the customer was billed an overtime rate for some of the work performed?

No, it doesn't. What the customer is billed has nothing whatsoever to do with what hours you work or what rate you get paid.