I hope this would help you ....
Chat User : If the I-485 and I-140 are pending for more than 6 months, can we change the company? If so, what would happen to the I-140 if there is an RFE?
Attorney Murthy : As you know, the INS has not yet issued any regulations on AC21 with respect to pending I-140 petitions. There is likely a risk that if the I-140 is denied or the INS issues an RFE the employer is not likely to respond, which could end the GC process for the AOS applicant. The safest course is to at least wait until the I-140 is approved before changing employers, since the INS may determine that without the
I-140 the I-485 cannot stand on its own feet.