A group of atheists has filed a lawsuit claiming the display of the World Trade Center cross at the 9/11 memorial in lower Manhattan is unconstitutional, calling it a "mingling of church and state."

The American Atheists, which advocates an "absolute separation" of government and religion, filed the lawsuit Monday to stop the display of the cross, arguing that it should not be included if "no other religions or philosophies will be honored," according to a statement on the group's website.

The cross, which consists of two intersecting steel beams that were found intact in the rubble at Ground Zero, was initially constructed on a side of a church in lower Manhattan. The cross was then placed inside the 9/11 Memorial Museum during a ceremony over the weekend.

"The WTC cross has become a Christian icon. It has been blessed by so-called holy men and presented as a reminder that their god, who couldn't be bothered to stop the Muslim terrorists or prevent 3,000 people from being killed in his name, cared only enough to bestow upon us some rubble that resembles a cross," the group's president, Dave Silverman, said in a press release. "It's a truly ridiculous assertion."

The National September 11 Memorial and Museum at the World Trade Center Foundation, Inc., is exempt from federal income tax. The organization's revenue in 2010 totaled nearly $90 million, of which $70 million was provided by government grants.

But museum organizers say the cross, which is a symbol of hope for many, should have a place at the memorial.

The cross is "an important part of our commitment to bring back the authentic physical reminders that tell the history of 9/11 in a way nothing else could," 9/11 Memorial president Joe Daniels said Saturday, the Christian Post reports.

"Its return is a symbol of the progress on the Memorial and Museum that we feel rather than see, reminding us that commemoration is at the heart of our mission," Daniels reportedly said.