Can I work full time for company A and concurrently work (part time) for Company B

[sdr22]

Hi,
I work full time for a company A. They hold my H1B. A Company B has a project for 7 months. Can I by any means work for company B on a part time H1B basis as well as maintain full time employment with compnay A? What are the legal issues involved? IS this at all possible??

thanks in advance