Early-morning preparations continue for U.S. president-elect Barack Obama's inaugural reviewing stand on Pennsylvania Avenue in front of the White House on Wednesday, Dec. 31, 2008. (Ron Edmonds/Associated Press)

A group of atheists is taking legal action in hopes of having all religious references removed from U.S. president-elect Barack Obama's inauguration ceremony in January.

A lawsuit filed in Federal Court is trying to prevent having the phrase "So help me God" included in the oath of office. It also wants to prevent inaugural prayers from being delivered at the event.

"We're hoping to stop prayer and religious rituals at governmental functions, especially at the inauguration," Dan Barker, co-president of the Freedom From Religion Foundation, told Fox News Radio.

"The inauguration is not a religious event. It is a secular event of a secular country that includes all Americans, including those of us who are not Christians, including those of us who are not believers."

Barker has teamed up with Michael Newdow to file the suit. Newdow unsuccessfully sought to have the words "under God" removed from the Pledge of Allegiance and sued to remove religion from inaugurations in 2001 and 2005.

There are 18 plaintiffs in total, including atheist and humanist organizations.

Prayer scheduled

Obama has chosen Pastor Rick Warren, the founder of a California mega-church, to deliver the inaugural invocation on Jan. 20 in Washington, D.C.

United Methodist Rev. Joseph Lowery, co-founder of the Southern Christian Leadership Conference, will also offer a benediction.

Pastor Rick Warren, at a book-signing in New York on Dec. 3, 2008. President-elect Barack Obama's choice of Warren to deliver the inaugural invocation drew one kind of protest. Whether the evangelical pastor offers the prayer in the name of Jesus may draw another. (Charles Sykes/Associated Press)

Warren wouldn't indicate Tuesday whether he plans to dedicate his prayer to Jesus Christ, saying only, "I'm a Christian pastor, so I will pray the only kind of prayer I know how to pray.

"Prayers are not to be sermons, speeches, position statements nor political posturing. They are humble, personal appeals to God," Warren wrote in a statement sent to the Associated Press.

Newdow's previous lawsuit had claimed an inaugural prayer was an unconstitutional endorsement of religion.

Could be sore point

Some members of the religious community in the U.S., however, said the absence of holy blessings would be a sore point for conservative Christians.

"If Rick Warren does not pray in Jesus' name, some folks are going to be very disappointed," said Kirbyjon Caldwell, who delivered a prayer at George W. Bush's swearing-in in 2001.

"Since he's evangelical, his own tribe, if you will, will have some angst if he does not do that."

Obama's oath of office will be administered Jan. 20 by Supreme Court Chief Justice John Roberts, just before Obama gives the country's 56th inaugural address.

The inauguration festivities will span four days, from Jan. 18 to 21. Events will include a Jan. 20 inauguration parade with dozens of marching bands from across the U.S., including two from Obama's high school in Honolulu.

Former vice-president Al Gore will be the honorary chairman of the 2009 Green Inaugural Ball on Jan. 19 at the National Portrait Gallery.

The inauguration of the first black U.S. president is expected to draw millions of visitors to the U.S. capital.

With files from the Associated Press