if you want to work with your sponsor. you should let them know that any time they want you can start working for them because you received your work permit.

If it is EB3 unskilled, let them be Find a good job and do if your employer doesn't contact you You do not have to work for your employer before I485 approval... what matters is you being in good standing with your employer And depending on your priority date... if you start with your employer now, you will be there for 2 to 4years

@USCIS IS A MESS INDEED!!!!

you need to let your employer know cos they have no idea about the work permit. they have no connection with USCIS