PHILADELPHIA (AP) August 1 -- The Internal Revenue Service should investigate the tax-exempt status of a Philadelphia church whose pastor is vocally endorsing George W. Bush for president, a church watchdog group says. The Rev. Herbert Lusk, pastor at Greater Exodus Baptist Church, appeared via video feed from inside the church Monday at the Republican National Convention to speak glowingly of the Texas governor. "We are supporting Governor Bush, and we are supporting him because we know that he understands that we must give faith a chance," Lusk said, according to transcripts of the speech. Churches and other nonprofit groups that are exempt from federal taxes under section 501(c)(3) of the tax code cannot endorse or oppose candidates for public office. They risk losing that status if they do so. Americans United for Separation of Church and State, a watchdog group based in Washington, said in a letter to IRS Commissioner Charles Rossotti that the comments may warrant an investigation. "It appears that Reverend Lusk has violated federal tax law by announcing that we, meaning his church, are supporting candidate Bush," said Barry Lynn, executive director of the organization. Lusk did not immediately return a telephone call Tuesday to his church. IRS officials declined comment on the letter, but the agency recently warned nonprofit groups to be careful in getting into politics. "These organizations cannot endorse any candidates, make donations to their campaigns, engage in fund raising, distribute statements or become involved in any other activities that may be beneficial or detrimental to any candidate," said that IRS statement. In practice, however, there are many gray areas, particularly in cases involving distinctions between individuals and the organizations they represent.