The Baltimore-based National Association for the Advancement of Colored People, the nation's largest civil rights organization, has refused to turn over documents for an Internal Revenue Service investigation into allegedly improper political activity, claiming the probe is politically motivated, USA Today reports.

In a letter sent to the IRS Friday, the NAACP cited what it contends is evidence that the agency launched the audit before the November election because of political pressure. IRS Commissioner Mark Everson, in a November letter to two congressional Democrats, said his agency began investigating several dozen nonprofit groups based in part on complaints from two members of Congress, whom he did not identify. The IRS notified the NAACP of the audit on October 8, telling the group that its tax-exempt status was in jeopardy because its chairman, Julian Bond, had attacked President Bush in a speech to the group's national convention in July. The NAACP received a summons on January 14 for information related to the speech, but in Friday's letter declined to comply.

"It appears that political pressure, rather than any sound legal authority, motivated the Service" to open the audit, said NAACP lawyers Lloyd Mayer and Marcus Owens in the letter. Owens is the former head of the IRS office that oversees tax-exempt organizations.

The IRS denies any partisan motive for the probe, which, according to Treasury Department spokesman Rob Nichols, is targeting "a wide array of groups across the political and ideological spectrum."