Do I need to re-enter USA if I was in India during visa transfer for new employer?

[BeeKay]

Dear Experts,

I am working with employer "A" and employer "B" filed my H1B transfer. I am planing to travel to my home country while the transfer is in progress.

Now if I re-enter USA using my current Visa and I-797 (from Employer "A"), both are valid till 10/2013 and resign to my current employer "A" after re-entering USA, do I need to go out of USA again (Canada/México) and re-enter using Employer "B" I-797 before joining Employer "B"? or Can I just resign from Employer "A", serve notice period and start working for employer "B"?

Note: My H1B visa transfer with Employer "B" will be approved while I am in India but I plan to re-enter USA using Employer "A" visa and I-797.

Thanks a lot for your time and suggestions.

[Attorney_10]

Generally, an H1B worker must present a valid approved H1B petition (I-797) for the company which they plan to work for upon entering the U.S. (i.e. if you plan to work for company B upon your return to the U.S. you must enter using company B's approval notice). The timing of when the new petition is filed and approved as well as your travel dates can impact whether you would need to travel outside the U.S. before beginning work with company B. Please schedule a consultation with an experienced immigration attorney to discuss the specific facts of your case.

[BeeKay]

Dear Attorney_10,

Thanks for a quick response.

I am planning to join employer "A" after coming back and that's the reason of using their I-797 and visa for re-entering USA after my India trip. Now once I am in, I plan to resign asap and serve the notice period to employer "A" before joining employer "B", whose I-797 was approved while I was in India.

So, in that case, do I need to go out of USA again (Canada/México) and re-enter using Employer "B" I-797 before joining Employer "B"? or Can I just resign from Employer "A", serve notice period and start working for employer "B"?