Over 30 current and former Democratic lawmakers filed a new amicus brief Monday supporting Consumer Financial Protection Bureau Deputy Director Leandra English to be reinstated as acting director of the agency.

The brief, which included Sens. Sherrod Brown and Elizabeth Warren as well as former lawmakers like Barney Frank and Chris Dodd, argues that Congress intended for the CFPB to be an independent agency, a status that they say was threatened when President Trump named Mick Mulvaney, the director of the Office of Management and Budget, to also be the acting director of the CFPB.

Democrats had filed an earlier brief in support of English's temporary restraining order request to halt Mulvaney's appointment. A judge denied that order, validating Mulvaney as the current acting director, but a full ruling on the merits of English's case is still pending. Arguments in the case are scheduled to be heard Dec. 22.

“The Dodd-Frank law is clear that Deputy Director English is the legal acting director," said Sen. Sherrod Brown, D-Ohio. Bloomberg News

English cites provisions in the Dodd-Frank Act as supporting her argument that the agency's deputy director is the de facto director in the absence of a Senate-confirmed leader. But the White House has claimed the Federal Vacancies Reform Act of 1998 gives Trump broad authority to name agency heads.

"The President’s purported appointment of Mulvaney is unlawful, and Deputy Director English is the lawful acting director of the bureau," the amicus brief stated. "Dodd-Frank’s mandatory and unqualified successor provision displaces the FVRA as the means by which a vacancy in the position of bureau director may be filled temporarily."

English was tapped on Nov. 24 to lead the agency by former CFPB Director Richard Cordray on his last day before resigning. On Nov. 29, she sued both Trump and Mulvaney, seeking a preliminary injunction to be reinstated as the CFPB's acting director.

The Democrats' latest amicus brief stated that allowing Mulvaney to be acting director "would plainly undermine the independence that was so critical to Congress’s plan in designing the bureau."

"By using mandatory language to inscribe this order of succession in statute, Congress supplanted the [Federal Vacancy Reform Act's] procedures for temporarily filling vacancies," the amicus brief stated. "After all, as Congress recognized at the time, those procedures would permit the president to hand-pick an acting director without the check of Senate confirmation, allowing that acting director, no matter how close his ties to the president, to head the bureau for many months."

Frank and Dodd have already sharply criticized Mulvaney's appointment at the helm of the agency.

Brown, the ranking member of the Senate Banking Committee, said the White House "must follow the law."

“The Dodd-Frank law is clear that Deputy Director English is the legal acting director, and she must be allowed to continue the agency’s work standing up for working families against financial abuse until a permanent director is confirmed by the Senate,” Brown said in a press release. “The White House must follow the law and nominate a permanent director swiftly who will fight for working people instead of the lenders that cheat them.”