A federal appeals court is ordering American Atheists to better explain its claim that the Ground Zero Cross is offensive and violates group members’ constitutional rights. The group is trying to keep the artifact out of the National September 11 Museum.

Read background from FoxNews.com:

The 17-foot-tall, steel beam “cross” was found in the rubble of the World Trade Center twin towers in New York that fell during the Sept. 11 terror attacks.

The cross became a sort of shrine or place of comfort for first responders who often prayed there and left messages or flowers. It was moved away from the debris a few weeks later and became a tourist attraction through several years of reconstruction.

American Atheists filed the suit in 2011, which was thrown out last year by a federal judge in the Southern District of New York.

The appeals court ruling Thursday cites an amicus brief filed by the Becket Fund for Religious Liberty, a nonprofit law firm that specializes in church-state law and protecting the free expression of all religious traditions.

“We’re thrilled that the court picked up on this issue,” said group lawyer Eric Baxter, whose brief argued that American Atheists had no right to bring a lawsuit in the first place. “Courts should not allow people to sue just because they claim to get ‘dyspepsia’ over a historical artifact displayed in a museum.”

The museum officially opened on May 21.

The judge has now given the plaintiffs until July 14 to file supplemental legal briefs before deciding whether the case will proceed. Among the questions that must be answered in the new filings is how the offensiveness of the cross, which the plaintiffs view as a Christian symbol for all 9-11 victims, becomes a “constitutional injury.”

The other question is -- if the plaintiffs indeed feel displaying the cross “marginalizes them as American citizens” -- then how is that a “particular and concrete injury" compared to just “the abstract stigmatization of atheists generally.”

The judge has also asked the plaintiffs to substantiate their claim the museum and Sept. 11 memorial are getting taxpayer dollars.