BALTIMORE – Several Republican members of Congress sent letters to the Internal Revenue Service questioning whether the NAACP had veered into political advocacy and asked for an investigation into its tax-exempt status, according to documents released by the civil rights organization.

The IRS began looking into the Baltimore-based National Association for the Advancement of Colored People about a month before the 2004 presidential election after a speech by the NAACP chairman, Julian Bond, that was largely critical of President Bush’s policies.

Political campaigning is prohibited under the NAACP’s tax-exempt status. The IRS said its inquiry would focus on whether Mr. Bond’s speech was too political, and that the investigation is among dozens into the activities of tax-exempt groups during the 2004 election season.

The NAACP received more than 500 pages of documents the IRS has gathered to begin its inquiry. The group had made requests under the Freedom of Information Act and provided the documents to the Baltimore Sun.

The documents include letters that members of Congress sent to the IRS on behalf of their constituents. The lawmakers include Senators Alexander of Tennessee and Collins of Maine, Rep. Jo Ann Davis of Virginia, the late Senator Thurmond of South Carolina, and two former congressmen, Larry Combest of Texas and Joe Scarborough of Florida. All are Republicans.

The NAACP has called the IRS audit a political smear campaign. An attorney for the NAACP, Marcus Owens, said the letters from Republican politicians raised questions about the motivation of the IRS probe.

“It’s clear that the NAACP drew a lot of criticism and complaints from the Republican Party, and many of the complaints don’t have a lot of substance to them,” he said. “The circumstances of the audit came just weeks before the election, and apparently they were triggered from members of the Republican Party at some level.”

The chief fund-raiser to Governor Ehrlich of Maryland wrote a letter asking for an IRS investigation shortly after the 2000 presidential campaign, the documents showed. Mr. Ehrlich was a congressman at the time.

Richard Hug said his letter was prompted by a television ad sponsored by the NAACP’s National Voter Fund. In it, the daughter of James Byrd, a black man dragged to death by three white men in a pickup truck, faulted then-Governor Bush of Texas for refusing her pleas for a hate crime law.

“I was acting as a citizen, and I think that everyone else ought to be concerned if they have nonprofit status and they are using political ads,” he said Wednesday.