Sen. Elizabeth Warren on Friday accused the acting head of the Consumer Financial Protection Bureau of undermining President Donald Trump’s stated push to make credit cards more affordable, according to a letter obtained exclusively by CNBC.

In a letter to acting CFPB Director Russell Vought, Warren, D-Mass., noted that in the last year the agency has dropped a rule limiting credit card late fees, sided with lenders in lawsuits over deceptive practices and paused enforcement actions against the industry.

Earlier this month, Trump demanded in a social media post that U.S. banks voluntarily cap credit card interest rates at 10% for a year. When they didn’t, Trump this week called on lawmakers to pass legislation on the issue.

“I spoke with President Trump last week and told him that Congress could pass legislation to cap credit card rates, if he would fight for it,” Warren wrote in her letter to Vought.

“While Congress considers legislation to address the issue, your own actions are directly undermining the President’s stated goals,” she wrote. “Under your leadership, the CPFB has taken steps to make it easier—not harder—for big banks and credit card companies to rip off Americans.”

The letter from Warren seizes on Trump’s pivot to affordability and seeks to leverage his initiative against his own administration, escalating tensions over the financial regulatory agency that she helped to create under the Obama administration. Members of the Trump administration have sought to shutter the CFPB as part of a broader pro-business deregulatory agenda.

Current and former CFPB employees have said the agency is on life support under Vought, who has fought in court to enact mass layoffs and stop the agency’s funding.

An agency spokesperson said that the CFPB was disallowed from limiting credit card rates by the Dodd Frank Act.

Vought should be “using the full scope of (the CFPB’s) authorities to address excessive credit card costs and to crack down on bad actors,” instead of trying to dismantle the agency, Warren wrote.

She directed Vought to “immediately reinstate its rule capping credit card late fees at $8, which would save Americans more than $10 billion annually,” Warren said.

She contended Vought should also tamp down on deceptive practices around the industry’s deferred interest promotions, resume enforcement of rules around monitoring interest rate increases, respond to a mounting pile of consumer complaints, and halt bait-and-switch tactics with rewards programs.

“Either President Trump is not serious about making credit cards more affordable or you are insubordinately disregarding his direction,” she wrote.