An aide says Congresswoman Nancy Boyda voted against a tax relief bill because it would increase the federal budget deficit.
But Republicans say the Democratic lawmaker is breaking promises to support tax relief for the middle class.
Boyda, representing the 2nd District of eastern Kansas, was one of only 30 House members to vote no Wednesday.
It reins in the alternative minimum tax and saves more than 20 million taxpayers from a tax increase averaging about $2,000.
But Thomas Seay, Boyda's re-election campaign spokeswoman, noted Thursday that the legislation would add nearly $65 billion to the budget deficit.
He said Boyda supports tax relief but, "We just can't throw fiscal responsibility out the window to do it."