Important note of caution on AC-21 for cinci2002 and everybody else!
there is this common misconception among folks that you can utilize AC-21 to change jobs after GC approval.
that is simply not true!
while some other aspects of AC-21 might still not be clear, it is clear in this respect: AC-21 is available ONLY while your i485 is pending. this might sound strange, but studying AC-21 in some detail explains that:
the portability available under AC-21 is actually the portability of the approved I-140 that underlies the I-485, not of the I-485 itself. and this portability kicks in when the I-485 has remained unadjudicated for > 180 days.
when you use AC-21, essentially what happens is that your new employer "inherits" your approved I-140, and becomes your sponsoring employer. When your employment-based I-485 is approved, it recognizes and "locks in" your new employer as your sponsoring employer.
also, as soon as your green card is approved, the I-140 (and the I-485) become meaningless, i.e. they "go out of scope" to use IT terminology
, therefore the AC-21 PORTABILITY ASSOCIATED WITH THEM IS ALSO NOT AVAILABLE ANY MORE.
this is in keeping with the theory of employment-based green cards: they are approved on the basis of offer/availability of permanent employment. so once your GC is approved, you have to demonstrate your intent to stay with your sponsoring employer by not leaving very soon, which in case you have used AC-21, is your new employer.
in other words, you may change employers by availing of AC-21 before GC approval, but not afterwards!