Originally Posted by
idliman
GC is given for a future job. While doing PERM, you put your signature in ETA 9089 form saying that your info (education) and past experience are true and correct. Then while submitting I485 Supp J (first time), you sign saying that you intend to accept the job offer. The employer signs saying that they offer you the job. So GC is provided based on a contract between you and the employer.
Now, anytime you change a job it is preferable to submit a new I485 Supp J and let USCIS review the job for AC21 portability provision. In reality, some people change jobs multiple times before their GC is adjudicated. So most attorneys will say that wait for a RFE from USCIS and then submit I485 Supp J. Moreoever, there is no requirement in the law that everyone should submit I485 Supp J proactively or everytime one changes a job using AC21. It is the last job that you work before getting the GC that matters. This is just a choice issue. You want to think that every job is your last job before getting GC (OR) actually wait for FA dates to be current and then do a I485 Supp J.
Now that we have straightened the whole GC process, USCIS can ask anytime a) for simple confirmation that you intend to work in the GC job (after getting GC) or b) ask for a new I485 Supp J. USCIS should NOT approve any GC without making sure that this contract is clear to them. But sometimes they do approve GCs without confirming this contract or assume that you are going to work for the PERM employer. While this may cause headaches later on during N400, most people just don't pay attention to it. USCIS having to deal with millions of illegal immigrants and huge rush of applicants, simply does not have the resources to come after you. Simply you are a small fish and they have much bigger fish to fry.
If it was me, I would submit Supp J and want to get GC based on the job that I am going to work on after getting GC for a "reasonable" time.
Hope this helps.