A group of House Democrats is urging President Barack Obama to nominate a permanent director for the Federal Housing Finance Agency to replace an acting chief they say is standing in the way of aid for struggling borrowers.

The 45 lawmakers led Representative Elijah Cummings of Maryland, the top Democrat on the House Oversight and Government Reform Committee, said in a letter to Obama that FHFA Acting Director Edward J. DeMarco should be removed because of his refusal to use U.S.-owned mortgage firms Fannie Mae and Freddie Mac to provide loan modifications including principal reduction.

“Ensuring that FHFA implements congressional directives to support the most liquid, efficient, competitive and resilient housing finance markets is a matter of national urgency,” the lawmakers wrote in the letter dated today. “For these reasons, we strongly urge you to nominate an FHFA director who is ready to fulfill this mission and address the many challenges still facing the nation’s housing finance markets.

DeMarco took charge at FHFA, which has overseen Fannie Mae and Freddie Mac since they were placed under conservatorship in 2008, when James Lockhart stepped down in 2009 amid debate over the future of the mortgage-finance firms that remains unresolved. Obama’s nomination of Joseph Smith, a former North Carolina banking regulator, was blocked by Senate Republicans.