Closing without a cleared 4506 form

Hi,
My sister and I are jointly buying a home the conventional way and last week we signed the closing papers at the title company.

We have still yet to close because the lender is waiting for a cleared 4506 form from the IRS for 2013 taxes.

The IRS can take 6 to 8 weeks to release this! We have shown them our 2013 W-2’s, proof from our CPA and countless docs and letters. Not to mention they have $100k sitting in the escrow acct for our down payment. It is board-line absurd that after signing the papers, this is what they are holding it up for!

Our concern is that the sellers will not want to wait and will sell to someone else.

My question: is the 4506 form the Lenders request or is it mandated from the government since this is FannyMae/Freddie Mac loan? Can they do this or do we have any recourse?

Look forward to any thoughts/ideas you may have to close this quickly.

Thank you in advanced for your time.
Anne