Senator Elizabeth Warren has accused acting Consumer Financial Protection Bureau Director Russell Vought of actively undermining President Donald Trump's stated goal of making credit cards more affordable, according to a letter obtained by CNBC.

In the sharply worded letter, Warren (D-Mass.) noted that under Vought’s leadership, the CFPB has dropped a rule capping credit card late fees at $8, sided with lenders in lawsuits over deceptive practices, and paused enforcement actions against the industry.

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

The criticism comes after Trump recently called on banks to voluntarily cap credit card interest rates at 10% and, when they refused, urged Congress to pass legislation on the issue. Warren told Trump last week that Congress could act if he supported the effort.

Warren demanded Vought "immediately reinstate" the late fee cap—which she said would save Americans over $10 billion annually—and crack down on deceptive industry practices.

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

The CFPB spokesperson responded that the agency is prohibited by the Dodd Frank Act from limiting credit card interest rates.