Do I need to send a 1099 form for a back charge?

Explain what you mean by "back charge".   To whom ?   For what reason ? 

I'm a subcontractor for a steel fabrication shop and I made a mistake on a job and was back charged $2000. My PO was paid in full and I sent the fabricator a check for the $2000. 

No you do not need to issue a 1099 ... this is handled by entering all of the income from the PO and then reporting the "return" on the Sch C.