SAN ANTONIO -- An atheist has filed a lawsuit aimed at preventing the mayor of San Antonio from proclaiming the National Day of Prayer on the steps of City Hall.

Patrick Greene, who filed the lawsuit in federal court Oct. 24, said Tuesday that the ceremony is exclusive to Christians and leaves out other faiths.

"If they allowed people of different faiths, Mormons, Muslims, Jehovah's Witnesses, Catholics and everybody else to be a part, that would be different. But they do not," he said. "It shows favoritism and preference, and the government shouldn't be in the business of doing that."

In a letter e-mailed to Mayor Phil Hardberger and City Attorney Michael Bernard, Greene said that the participation of the mayor and City Council is a violation of the U.S. Constitution.

"It would give the passer-by the idea that the government, which represents all citizens, gives preference to one religion over another, and that's a direct stab at the establishment clause of the constitution," Greene added.

Hardberger and Bernard didn't immediately return phone calls to KSAT 12 News.

The organizer of the prayer event said, "this is a legal matter, and it just has to play itself out."

The next National Day of Prayer is scheduled for May 7, 2009.