The presidential campaign of Bernie Sanders has demanded the removal of two leaders from their positions on Democratic National Convention committees, calling them “aggressive attack surrogates” for likely Democratic nominee Hillary Clinton.

In a formal letter sent Friday, Brad Deutsch, the campaign’s legal counsel, asked that Connecticut Gov. Dannel Malloy and former Massachusetts Rep. Barney Frank be disqualified from their posts as co-chairman of the Platform Committee and co-chairman of the convention’s Rules Committee, respectively.

“Their criticisms of Senator Sanders have gone beyond dispassionate ideological disagreement and have exposed a deeper professional, political and personal hostility toward the Senator and his Campaign,” Deutsch wrote. “The Chairs therefore cannot be relied upon to perform their Convention duties fairly and capably while laboring under such deeply held bias.”

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The letter—addressed to the co-chairs of the DNC’s Rules and Bylaws Committee—argued that their support of Clinton would cause Malloy and Frank to “exclude meaningful input from supporters of Senator Sanders’ candidacy.” The letter detailed instances when both had criticized Sanders.

“It is inconceivable to me that anything could come before that committee that will affect who the nominee is,” Frank said in response to the accusations, Politico reported. “I think what you have here is this: Sanders is losing to Hillary Clinton because she is getting many more votes and many more pledged delegates. Some of [the Sanders supporters] are trying to lay the claim that he’s being unfairly deprived of this.”

In a response letter on Saturday, the Rules and Bylaws Committee co-chairs dismissed the challenge from Sanders and said Malloy and Frank had not violated any DNC rules.

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Write to Katie Reilly at Katie.Reilly@time.com.