(RNS) Five Texans are suing Gov. Rick Perry to prevent him from appearing at a prayer rally scheduled for Aug. 6 in a Houston stadium.

The federal suit alleges that Perry, a Republican, is violating the separation of church and state by appearing in a promotional video for a prayer gathering organized by several evangelical groups.

The suit also seeks the removal of a link from the governor's state-run website to the rally's website.

Billed as "The Response: A Call to Prayer for a Nation in Crisis," the rally's website lists Perry as "the initiator," citing his proclamation of the day as one of "prayer and fasting for our nation's challenges."

The Freedom From Religion Foundation, a Wisconsin-based watchdog group, joined the suit filed by five Texans, who are identified by name as "nonbelievers."

"What he (Perry) is doing is beyond anything we've seen a governor do," said Annie Laurie Gaylor, co-president of FFRF. "It is his face you see when you go to the rally's website. It would not have happened without him. That is why we decided to sue."

Eugene Volokh, a professor of constitutional law at the University of California, Los Angeles, doubts the suit's potential. He said previous court rulings have recognized elected officials as individuals entitled to freedom of speech and religion.

"When a governor appears at an event, he is understood to be acting as both a person and a government official," Volokh said. "The courts have given these folks tremendous latitude in what they can say in their own statements."

Volokh said the suit could force Perry to remove the link to the rally from his official website, "but that would be a small victory."