Can old employer cancel my h1b after it has been transferred?

I am moving from employer A to employer B. Employer B had filed for h1b transfer under premium processing and has been APPROVED. I am joining Employer B in a week. Can Employer A cancel/revoke the h1b?

Yes, they can revoke their own approved petition. However, that will not impact B’s approved petition. You are still good to work w/ B.