U.S. Senator Elizabeth Warren urged President Barack Obama on Friday to replace Securities and Exchange Commission Chair Mary Jo White, saying she had undermined the agency’s investor protection mission.

Warren, a Massachusetts Democrat who advocates for strong financial regulation, also said in a letter to Obama that White had failed to develop a rule requiring publicly traded companies to disclose political spending.

Warren has been a vocal critic of White, an independent who was chosen by Obama in 2013, but this is the first time she has called for White to be removed as chair.

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“I do not make this request lightly,” Warren wrote to Obama. “The only way to return the SEC to its intended purpose is to change its leadership.”

She said Obama had the authority to choose one of the other two commissioners, both picked by the Democratic president, as the new chair. There are two vacancies on the five-member commission.