Sen. Elizabeth Warren (D-MA) spoke out Monday on President Donald Trump’s decision to install White House budget director Mick Mulvaney as acting director of the Consumer Financial Protection Bureau.

“This is about whose side President Trump is on — big banks, or working families,” Warren told the Washington Post’s Greg Sargent. “So far in his administration, he has chosen the big banks time after time. Is he going to stand up for the working families who helped elect him?”

The CFPB is in the midst of a crisis of leadership, reflected in a lawsuit Sunday night by newly elevated deputy director Leandra English, who had previously served as chief of staff to former CFPB Director Richard Cordray. Under the 2010 Dodd-Frank law, which authorized the agency in the first place, the deputy director becomes the acting director in the case of a vacancy. But the White House, in naming Mulvaney the acting director, cited the Federal Vacancies Reform Act. Currently, the agency effectively has two acting directors.

Mulvaney, who has said he is opposed to the agency’s very existence, has reportedly told CFPB staff to report communications from English to the agency’s legal department.

Warren has sided firmly with English, saying Dodd-Frank clearly states that she ought to be acting director. Warren was the driving force behind the agency’s creation as an adviser to the Obama administration. Reuters reported the senator would meet with English Monday.

“The agency deserves a leader who has a demonstrated track record of protecting consumers and standing up to Wall Street,” Warren told the Post. Keeping English in charge, she said, would give Americans “a chance to look at this agency one more time and see how hard it fights on behalf of consumers.”

Under Mulvaney, or someone like him confirmed on a permanent basis, Warren said, “The agency will be headed by someone who fundamentally doesn’t believe in its mission.”

“This would change every calculation that every giant bank makes in the executive suite when deciding just how close to breaking the law they want to come,” she continued. “If the cop is pulled off the beat, then the profits from cheating people look far more attractive to the banking executives.”

“It will be up to Senate Republicans to decide whether they want to put someone in the job who is firmly on the side of big banks,” she added.