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The NAACP (search), the nation's oldest civil rights organization, is refusing to cooperate with an IRS investigation into an allegedly improper political speech, charging that the timing of the probe was itself politically motivated.

The National Association for the Advancement of Colored People said in October that the group's tax-exempt status was under review after its chairman, Julian Bond (search), gave a speech that criticized President Bush.

In a letter to the IRS on Thursday, NAACP attorneys said the group will not hand over documents requested in the probe and argued that the IRS followed improper procedure by launching its exam before the group filed its 2004 tax return.

The letter said the tax examiners aimed to influence the group's activities just before the November presidential election.

"We must conclude that the intention was to chill appropriate voter registration and get-out-the-vote efforts, whether conducted by the NAACP or by other organizations that are targeted by similar examinations in the program," they wrote.

The IRS has said it's probing about 60 charities, churches and other tax-exempt groups for potentially breaking federal rules that bar them from participating in political activity.

In a letter to the House Democrats' top tax writer in November, IRS Commissioner Mark Everson said the agency received two letters questioning political activity of nonprofit groups from members of Congress. None came from the White House or any federal political appointee.

Federal law prohibits the IRS from discussing specifics of tax return information or audits, but IRS spokesman Terry Lemons said groups investigated for potentially improper political activity span the ideological spectrum.

"Law enforcement decisions at the IRS are made without regard to political considerations," he said. "Career civil servants, not political appointees, make these decisions in a fair and impartial manner."

The NAACP said the IRS challenged as improper campaign intervention a Bond speech this summer because it condemned the president's policies on education, the economy and the war in Iraq.

The civil rights group said it has a long history of criticizing presidents and their policies and that Bond criticized both political parties during the speech.

The IRS could request that the Justice Department ask a federal court to enforce the summons and hand over the requested documents.