GC Process Certification

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GC Process Continution

Dear Sir,

Here is my problem

Now Iam working for a company A and they filed my Labor verification in the part of GC process.
but I got another offer from Company B and they are asking me to transfer my H1 to their compnay(B). If I change my H1 to Compnay B, will the GC process stops?
But I will be back to my parent company(Company A) after 4 or 5 months. If I return back to Company A, shall I use my existing GC process? or The whole GC process is going to stop and need start it from scratch?

Please help me out from this H1 transfer situation..

Thanks a lot