Citizens for Responsibility and Ethics in Washington (CREW) filed a complaint with the IRS on Wednesday alleging that Grover Norquist's Americans for Tax Reform violated federal tax law.

"It appears ATR and Mr. Norquist declared less than half of the political activity it conducted in 2010 on its tax return," the complaint said. "Therefore, the IRS should investigate ATR and Mr. Norquist and, should it find they violated federal law, take appropriate action, including but not limited to referring this matter to the Department of Justice for prosecution."

CREW found that ATR spent more than $4.2 million on ads in 2010, which urged people to vote against a number of Democratic representatives. The independent expenditures were reported to the Federal Election Commission. But on its tax return, ATR claimed it spent only $1.85 million on political activities.

Tax-exempt organizations like ATR are required to disclose the amount they spend on political activities to determine whether they are complying with their tax-exempt status.

“Grover Norquist’s numbers just don’t add up,” said CREW Executive Director Melanie Sloan. “Americans for Tax Reform spent millions of dollars in 2010 trying to defeat candidates who disagreed with its agenda, then left most of that spending off its own tax return. Perhaps Mr. Norquist should sign a pledge that he won’t lie to the IRS about his group’s political activity."

Nearly every Republican in Congress has signed ATR's Taxpayer Protection Pledge, vowing to oppose any and all tax increases. Only 14 Republican members of 112th Congress have refused to sign the pledge.

When the 12-member deficit "super committee" was trying to reach a deal to raise the federal debt limit, Sen. John Kerry complained that Norquist was the 13th member of the committee.

“Groups like Americans for Tax Reform already don’t have to disclose their donors despite their heavy involvement in elections. The least we should expect is that they truthfully report their political spending,” Sloan added. “Given Mr. Norquist’s well-known interest in the tax system, surely he knew he couldn’t lie on his taxes. The IRS should investigate immediately.”

[Image via Gage Skidmore]