Pope Francis' visit to Philadelphia has almost everyone excited, including inmates at the city jail where he is scheduled to hold a mass on Sept. 26.

But one group isn't pleased that some of those inmates have been working on a chair for the Holy Father to sit in when he gets here — the atheist Freedom From Religion Foundation (FFRF)

In a "letter of protest" to Commissioner Louis Giorla issued by the FFRF, the group's co-president Annie Laurie Gaylor called the project a "misuse of prisoners" which violated prisoners' First Amendment rights "by honoring Catholicism's leaders above all others."

Related link: Staff, inmates jubilant over Pope visit to city jail 

"PPS [Philadelphia Prison Systems] must remain neutral toward religion in order to accommodate all inmates," Gaylor wrote. "By singling out Pope Francis, PPS appears to be endorsing his sectarian religious message."

Because PPS is a government agency, Gaylor argued, it must not show any favor toward any religion -- and the Pope chair could make non-Catholic inmates feel left out or like "outsiders," she wrote.

Related link: Guards allegedly smuggled drugs into city jail: feds

Prisons spokeswoman Shawn Hawes said the chair was built through a non religious program.

""The chair that was built by staff and inmates enrolled in an carpentry skills, job readiness industries program.  It is a program that prepares inmates, regardless of faith, to gain productive employment upon release," Hawes said in an email. She also denied the FRFF's accusation that the prison favors or discriminates against any religion.

"The inmates at the PPS are afforded the opportunity to practice whichever religion they choose while in custody," Hawes wrote. "Although there are chaplains on staff of all faiths to minister, no one is forced or compelled to participate in religious services or programming. Conversely, inmates are free to not practice religion while in custody as well."

A group of inmates who work within the woodshop at Philadelphia Industrial Correctional Center volunteered to create and refinish a walnut chair, which will be reupholstered by inmates at Curran-Fromhold Correctional Facility, where Pope Francis will deliver his mass to inmates.

Inmate-built furniture is sold to various city agencies for use, such as the Philadelphia D.A.'s office.

Note: This story was updated to include a response from the Philadelphia Prisons System.