The effort is one of several in support of Michael Griffin, who was dismissed by Holy Ghost Preparatory School, and they include a petition at Change.org that had drawn more than 7,500 signatures as of Monday.
"Michael Griffin did not deserve to be treated in a way that does not clearly reflect Christ and His teachings," says the letter sponsored by the Pennsylvania Student Equality Coalition. "He has dedicated his life to the Holy Ghost Community. He is just as much a part of the Holy Ghost family as any other member."
Griffin was dismissed after a Dec. 6 meeting with the school president, Fr. James McCloskey, and the principal, Jeffrey Danilak. Griffin had emailed Danilak earlier in the week to say he might be late for an in-service day because he was applying for a marriage license with his partner in neighboring New Jersey, where gay marriage became legal earlier this year.
Even though it was widely known in the school that Griffin -- who had taught at Holy Ghost for 12 years -- was gay, and he often appeared at events with his partner, McCloskey and Danilak said by seeking to formalize his relationship, Griffin had violated his contract.
"We regret the pain that this has caused to any and all involved," he added.
But the priest said because Griffin's action violated the terms of his teaching contract, "which requires all faculty and staff to follow the teachings of the Church as a condition of their employment," he had "no choice" but to fire him immediately.
Several Holy Ghost alums are also protesting.
Former student Dan McQuade wrote a column in Philadelphia magazine saying the action would lead to reduced support for the school, a private all-boys high school in Bensalem, Pa., operated by the Congregation of the Holy Spirit religious order.
"What McCloskey has done is tell gay students and alums that you're welcome in the community as long as you don't ask for the same rights as straight people," McQuade wrote.
Another Holy Ghost graduate, Zachary Nalbone, a student of Griffin's during the 2006-07 school year, also protested in a press release from the Human Rights Campaign.
"Mr. Griffin was one of the hardest-working and most dedicated teachers who undeniably embodied the spirit of Holy Ghost Prep," Nalbone said. He "deserved a better end to his tenure as a teacher at Holy Ghost, and I sincerely hope my alma mater will rectify this hasty decision."
The publicity over Griffin's firing is likely to complicate efforts by church leaders like New York Cardinal Timothy Dolan, who said this month that the bishops have been "outmarketed" on gay rights and "caricatured as being anti-gay."
But it's also likely that Griffin will not win his job back no matter how big the protests grow.
When a teacher at a Catholic high school in suburban Los Angeles was fired this summer for marrying his partner, it prompted an outpouring of support, including more than 90,000 signatures on a Change.org petition.
But the school maintained its stance and would not rehire the teacher, Ken Bencomo.
Gay and lesbian teachers aren't the only ones finding themselves under fire.
An unmarried couple in Lawrence, Mass., Sean Houlihan and Natalie Ferland, were fired from their jobs as teachers at a Catholic school after revealing that they were expecting a baby together.