Kumarash,
Once your labor is cleared through your first employer then you can file your I-140 automatically. My suggestion is that you should file with your current employer since that application will have a older PD than your PERM application. In the long run PD will become a crucial factor for 485 stage since the current retrogression is killing us all..
As I said before once your labor is cleared from either your current employer or future employer you will be in a position to file your 140.
Whichever labor gets approved first will kinda nullify your other labor application since you will have to file your 140 soon one way or the other. However I am not sure about how much time you can delay your 140 application once your labor has approved. This is a catch 22 situation and you have to play your cards carefully.
I would suggest you take professional help from a lawyer. You can also search thru' these forums to find out whether this query has been answered already or not. Rajiv Khanna might help you out.
Good luck !!!