HARRISBURG – For decades, the Pennsylvania House of Representatives, like most governmental bodies, has opened each session with a prayer.

But does it have to be delivered by someone who believes in a higher power?

That question is at the heart of a battle unfolding in a courtroom across the street from the  Capitol. There, members of the House are trying to shut down a legal challenge over who can deliver the invocation at public sessions, placing Pennsylvania in the middle of a debate over the rights of atheists and nonbelievers.

On Wednesday, lawyers for House Speaker Mike Turzai (R. Allegheny), as well as the chamber's parliamentarian and other lawmakers, asked a federal judge to dismiss a lawsuit by a group of atheists, humanists, and nonbelievers claiming discrimination because they have been blocked from giving the invocation at the start of legislative sessions.

House members told Judge Christopher C. Conner that their prayer policy is constitutional, stating clearly that members of a "regularly established church or religious institution" can deliver the invocation. Over the years, representatives from different faiths have been selected for the task, they said.

"If you hear from prayer-givers, must you hear from people who don't want to pray but will be respectful and solemnize your occasion? The Constitution says that you don't have to," said Philadelphia lawyer Mark E. Chopko of Stradley Ronon, who is representing House officials.

But five Pennsylvania residents and three organizations of atheists, humanists, and free-thinkers counter that the House has treated them like a "disfavored minority" because they do not believe in God.

They have applied to give the invocation, they said in the suit, but have been turned down. They also contend that once, two of their members who declined to stand during the session's opening prayer were pressured by Turzai and a House security guard to do so.

"Discrimination based on race, sex, national origin, disability, and sexual orientation has become prohibited or disfavored," states the lawsuit. "Nevertheless, in the House's eyes, people who do not believe in God remain a disfavored minority against whom it is acceptable to discriminate."

They are arguing the House's policy violates the free speech, equal protection, and establishment clauses of the U.S. Constitution.

 "Like people who believe in God, the plaintiffs have strong belief systems about what is right and wrong and how they should live their lives," the lawsuit states. "Like theists, the plaintiffs are capable of giving inspiring and moving invocations."

Conner did not immediately rule on the House's attempt to dismiss the suit.

The debate over legislative prayer and the rights of nonbelievers to give invocations at government meetings has gained attention and headlines in the wake of a 2014 U.S. Supreme Court ruling.

In a divided decision, the justices upheld the longstanding tradition of opening government meetings with prayer, even when a specific religion is favored. The case grew out of a lawsuit by two residents in Greece, N.Y., who argued the town's government regularly opened its meetings with Christian prayer.

Most legislatures open their sessions with prayer, according to the National Conference of State Legislatures. Though the policies vary, the general guidelines are that they be "nonsectarian, inclusive of all beliefs, and nonpolitical," said Brenda Erickson, a senior research analyst at the group.

The conference does not track how many legislative chambers allow atheists or nonbelievers to deliver legislative invocations.

The Pennsylvania Senate would make such a list. It allowed one of the plaintiffs in the federal legal challenge, Deana Weaver, to deliver an opening invocation.

"In my invocation, my appeal was to them as a higher authority to tolerate differences, to welcome diversity," Weaver said. "I invoked compassion and tolerance for LGBT, for clean air, clean water, for our military and police and fire and ambulance. I thought it was very motivating and something that is very akin to any other sort of religious prayer, no matter who your entity is."

Other governments have decided to do away with prayer. Last year, the City Council in Phoenix voted in a highly controversial move to replace the opening prayer with "silent prayer" after a group of Satanists signed up to deliver the invocation.