Sen. Kyrsten Sinema’s (D-Ariz.) opposition to Democratic plans to raise corporate or personal tax rates has infuriated the other members of her party, so much so that some of her advisers have resigned in protest of her position.

Five members of Sinema’s Veterans Advisory Council on Thursday wrote a letter to the senator blasting her for opposing parts of President Joe Biden’s $3.5 trillion reconciliation package and refusing to go along with a scheme to abolish the 60-vote requirement to overcome a filibuster and pass legislation in the Senate.

“You have become one of the principal obstacles to progress, answering to big donors rather than your own people. We shouldn’t have to buy representation from you, and your failure to stand by your people and see their urgent needs is alarming,” the Democratic veterans wrote in the letter, which was first reported by the New York Times.