dval_dpal, check your online status of I-485 - it may be an RFE....
But sometimes, I have heard news that these USCIS is a bit smarter at issuing RFE's.....instead of issuing an official RFE - they sometimes just call the lawyer's office and ask them to fax the required documents....
From the sound of it - if they asked for paystubs/w2 documents - it might be for I485 petition - I would not assume that it's for I140 petition....
For I485 - they commonly validate if the job offer is genuine...between employee and the employer....hence they usually ask for Employment Verification Job Offer Letter (EVL) and if possible, pay stubs/W2 to corroborate the job offer.....but pay stubs/W2 are optional - since for future employement offers ....they do not apply!
But, yep, I agree, sometimes USCIS is known to review all the underlying petitions, like LABOR/I-140 to validate them before issuing approval for I485....but that's very rare
But, in your case - it sounds more like RFE on I485....