Can I work for new employer while on leave of absence for the old employer?

I have H1B with Company A, I am wanting to start my employment with Company B (on H1B receipt). I have pending bonus money coming from Employer A. I will get that credited only if I stay for 2 more weeks with them. But Company B isn’t ready to wait for 2 more weeks and is wanting me to start immediately. Company A says I can go on leave of absence for 2 weeks if I want the bonus money. Actually I need this money to repay the sign on bonus I received when I joined Company A. My question is, can I work for Company B while on Leave of Absence with Company A. Is this legal in H1B? I think there will atleast be one overlapping PayCheck. Please advise.

You technically cannot be employed for two companies full time at the same time, unless it is a concurrent petition. One thing you can do is, ask company B to file H1B petition, it will take them anyways 2 weeks to file the petition with LCA taking a week and USCIS to send out receipt notice. By that time, two weeks would have passed. The day you get your receipt notice, you can leave Company A. Discuss with your attorney at Company B and make it work, it should be fine.

I already received the H1B transfer receipt for Company B. Thats why they are asking me to start ASAP.
Since I won’t be working with Company A and will be on Leave of Absence for the next 2 weeks, is it still not legal to start working for Employer B?

Well, ideally, you should have the relieving letter from them ( company A) stating that your last day is X day and then start working at Company B after that X day…I am not sure, how closely USCIS monitors these subtle changes in companies…some of the ways they would know is by the pay slips and I-9 form. Try to convince your employer B to wait for 2 weeks, if not make an informed decision by speaking to an attorney.