query: do mortgage underwriters contact the IRS

At closing, most mortgage lenders require that the borrowers sign an IRS form 4506 which gives them the right to obtain a copy of the borrower's income tax form.  Mortgage lenders DO contact the IRS routinely as part of a good quality control program.  It's a fraud prevention tool and they DO catch fraudsters using this method.

I strongly advise against falsifying tax forms used in a mortgage