American Atheists, the group that has been trying to remove the Ground Zero Cross from the National 9/11 Museum in New York, has been asked by a federal appeals court to explain why it finds the artifact to be "offensive," "repugnant," and a violation of the Establishment Clause.

"Plaintiffs' brief should, at a minimum, clarify both the injuries alleged and legal theories relied on to support standing," the Second Circuit Court of Appeals asked in an order late last week.

"Further, to the extent plaintiffs allege that they have been 'injured in consequence of having a religious tradition that is not their own imposed upon them through the power of the state,' First Am. Compl. because individual plaintiffs view use of the challenged 'cross, a Christian symbol, to represent all victims of the 9/11 Attacks' as 'offensive,' 'repugnant,' and 'insult[ing]' to them as atheists, plaintiffs should explain how such offense states a cognizable constitutional injury."

The secular organization has been appealing against the federal district court's decision to keep the 17-foot-tall Ground Zero Cross, which was fashioned by two steep beams recovered from the Twin Towers' collapse at the 9/11 memorial museum.

While the cross had become and emotional symbol for many in the aftermath of the attack, where close to 3,000 people were killed, American Atheists has argued that it alienates non-Christians seeking to commemorate the dead.

"The Cross also alienates those who wish to learn about events at the National September 11 Memorial & Museum," the group explains in its filing.

"The 17-foot tall Christian Cross is one of the largest objects in the Memorial. It dominates all other religious objects. The inclusion of information to accompany the Cross does not change the essential facts that in the present case the government is sponsoring and erecting an indisputably religious symbol which advances one religion above all other religions and non-religion as well."

The Becket Fund for Religious Liberty, one of the legal groups that has defended the Ground Zero Cross, argued in a brief that American Atheists had no right to file such a lawsuit in the first place, and praised the court's recent order.

"Courts should not allow people to sue just because they claim to get 'dyspepsia' over a historical artifact displayed in a museum," said Eric Baxter, Counsel for the Becket Fund.

"It is unusual for a court to require parties to a lawsuit to file additional briefs based on arguments raised by a non-party," Baxter added.

"Hopefully, this is a signal that the Court will draw the line against American Atheists' frivolous attack on the Ground Zero Cross. More importantly, we hope the Court firmly rejects the idea that the Constitution treats religion with suspicion and instead reaffirms that it protects the role of religion in the public square."

Other law groups, such as the American Center for Law and Justice, have also criticized in a brief what they say is American Atheists' attempts to "rewrite history."

"As the district court correctly held, it is entirely appropriate and lawful for the curators of a museum to acknowledge the Cross's actual, historic role by placing it in the September 11 Memorial Museum," Jay Sekulow, chief counsel of the ACLJ, said back in November.

"In the days and weeks following the September 11, 2001 terrorist attacks, the challenged World Trade Center Cross (the "Cross") had a widely documented and positive effect on the First Responders at the Ground Zero site," the legal group's brief contends.

"Offended observers (even observers whose offense is so great that they claim physical illness) cannot be permitted to rewrite history or constitutional precedent. Acknowledging history does not establish a religion, and Plaintiffs-Appellants' lawsuit is without merit."

The National 9/11 Museum officially opened to the public on May 21 following a dedication ceremony attended by President Barack Obama, along with dignitaries and families of the victims.