MADISON, Wis. -- A federal lawsuit filed by a Wisconsin-based group representing atheists and agnostics argues that the Internal Revenue Service is violating the U.S. Constitution by allowing tax-exempt churches and religious organizations to get involved in political campaigns.

The Freedom from Religion Foundation argues that churches and other religious organizations have become increasingly more involved in political campaigns, "blatantly and deliberately flaunting the electioneering restrictions."

Its lawsuit filed Wednesday in U.S. District Court in Madison argues that the IRS is not enforcing the federal tax code, which prohibits tax-exempt religious organizations from electioneering. Not enforcing it is a violation of the establishment clause of the First Amendment and a violation of equal protection rights because the same preferential treatment is not provided to other tax-exempt organizations such as the Freedom from Religion Foundation, the lawsuit contends.

The lawsuit, which was filed against IRS Commissioner Doug Shulman, asks that the court order Shulman to initiate enforcement of the electioneering restrictions against churches and religious organizations.

It also asks that the IRS initiate legal action against any churches or religious organizations that are believed to be violating the restrictions.

Churches and religious organizations obtain a significant benefit from their tax-exempt status while also being able to engage in electioneering that other similar tax-exempt organizations do not do, the lawsuit argues.

A spokesman for the IRS in Wisconsin declined to comment.

The lawsuit cites full-page ads run this fall in the New York Times and other newspapers by the Billy Graham Evangelistic Association that featured a photo of renowned evangelist Billy Graham urging Americans to vote along biblical principles. Graham met in October with Mitt Romney and pledged to do "all I can" to help the Republican presidential nominee.

The lawsuit also refers to an order from Roman Catholic Bishop Daniel Jenky of Peoria, Ill., requiring all the priests in his diocese to read a statement urging Catholics to vote and stating that, "Catholic politicians, bureaucrats, and their electoral supporters who callously enable the destruction of innocent human life in the womb also thereby reject Jesus as their Lord."

The lawsuit also refers to "Pulpit Freedom Sunday," a national event on Oct. 7 in which more than 1,500 pastors endorsed a candidate from the pulpit and then sent a record of their statement to the IRS, hoping their challenge would eventually end up in court.

The Alliance Defending Freedom, a conservative Christian legal organization based in Scottsdale, Ariz., has organized the event since 2008. The group considers the IRS regulations against bringing partisan politics to the pulpit an unconstitutional government intrusion.

For the past three years, the IRS hasn't been investigating complaints of partisan political activity by churches, leaving religious groups who make direct or thinly veiled endorsements of political candidates unchallenged.

The IRS monitors religious and other nonprofits on everything from salaries to spending, and that oversight continues. However, Russell Renwicks, a manager in the IRS Mid-Atlantic region, said in October that the agency had suspended audits of churches suspected of breaching federal restrictions on political activity. A 2009 federal court ruling required the IRS to clarify which high-ranking official could authorize audits over the tax code's political rules. The IRS has yet to do so.

The Freedom from Religion Foundation, which says it has 19,000 members nationwide, frequently files lawsuits challenging potential violations of the separation of church and state.

In recent years it has challenged the legality of the National Day of Prayer, the placement of a cross on a war memorial in Rhode Island, and praying before sporting events and other activities at the University of Tennessee.

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