Most of the non-immigrats in USA will plan to move from current employer once the i-140 is approved. There are lot of thing s that person is on H1b visa should care about before switching employers.

Moving employers requires new Labor and I-140

This article talks about risks associated with moving employers with approved I-140.You might think after moving to a new employer, i-140 from previous employer will be carried automatically. But the fact is the new employer needs to file labor and i-140 from scratch to process your greencard.

You may lose priority date

If the old employer cancels i-140 before the i-140 with the new employer gets approved, you will loos the priority date. New employer can't get the old priority date.

Impact on H4-EAD

If old employer cancels I-140 before the new employer's i-140 gets approved your spouse's H4-EAD will be cancelled. You need to wait until new employer's i-140 gets approved to get a new H4-EAD.