A Wisconsin-based religious freedom group is suing Texas Gov. Rick Perry, a possible Republican presidential contender, in an effort to block his promotion of and participation in an all-day Christian prayer event to be held Aug. 6, arguing that it violates the constitutional separation of church and state.

The Freedom From Religious Foundation, which claims more than 16,000 members, including 700 in Texas, filed the federal lawsuit Wednesday in Houston, contending that Perry’s actions violate the Constitution's Establishment Clause by “giving the appearance that the government prefers evangelical Christian religious beliefs over other religious beliefs and non-beliefs.”

“We always say, beware prayer by pious politicians,” said Annie Laurie Gaylor, who co-directs the group with her husband, Dan Barker, a former evangelical Christian minister who is now an atheist.

“Nothing fails like prayer,” she said. “It’s the ultimate political cop-out.”

The lawsuit, which comes as Perry flirts with joining the field of GOP presidential contenders, notes that the plaintiffs are “nonbelievers who support the free exercise of religion, but strongly oppose the government establishment and endorsement of religion, including prayer and fasting, which are not only an ineffectual use of time and government resources, but which can be harmful or counterproductive as a substitute for reasoned action.”

Perry’s office shrugged off news of the lawsuit.

“Governor Perry has been looking forward to the Aug. 6 prayer event, which continues to move forward as planned,” Perry’s office said in a written statement. “He believes it will serve as an important opportunity for Americans to gather together and pray to God, seeking his wisdom and guidance as our nation navigates the challenges before it. The pending litigation will not affect plans for the prayer event.”

The event has been described as a non-denominational, apolitical, Christian prayer meeting hosted by the American Family Association at Reliant Stadium in Houston. The website for the event is linked from the governor’s official website and includes a videotaped invitation from Perry.

Perry has invited every governor in the country to attend the event, which encourages people to bring a Bible and a notebook. He has also urged them to issue proclamations, making Aug. 6 a day of prayer.

“The answers for America’s problems won’t be found on our knees or in heaven, but by using our brains, our reason and in compassionate action,” Barker said. “Governor Perry’s distasteful use of his civil office to plan and dictate a religious course of action to ‘all citizens’ is deeply offensive to many citizens, as well as to our secular form of government.”

Perry has mixed religion with politics before. In April, he called on all Texans to pray for rain for three days as most of the state battled an extreme drought that led to massive wildfires that scorched more than a million acres this year, claimed the lives of two firefighters and destroyed nearly 400 homes.

He also joined three other Gulf Coast state governors – Bobby Jindal in Louisiana, Haley Barbour in Mississippi and Bob Riley in Alabama – last year for a day of prayer more than two months after the BP oil spill.