Question: "Hi I'm working for Company A and it has filed for my H1B, but has received RFE (the decision is till pending). now company B had filed for H1B visa too and got approved. Can I transfer company B's approved H1B to company A, if Company A's visa gets denied. Please advise."
Answer: H-1B petitions are specifically tied to the employer. As a result, you cannot work for Company A, unless you have an approved H-1B petition for Company A. If you can acquire general work authorization, such as through a pending green card process, you might have more flexibility as to your employer, but otherwise you are limited by the H-1B requirements.