An Indianapolis high school is the target of a national secular society's ire after a teacher at the school said he was reprimanded for telling students they could opt out of the Pledge of Allegiance.

The American Humanist Association, an educational organization that advocates on the behalf of atheists, agnostics and religious minorities, sent a letter this week to Franklin Central High School. In it, the group called on the school to allow teachers to inform students of their free speech rights, including nonparticipation in the pledge.

If not, the group's legal center would be made available to teachers, the letter said.

The school did not respond to IndyStar's requests for comment.

"The mission of AHA’s legal center is to protect one of the most fundamental principles of our democracy: the First Amendment rights to free speech and religious liberty," the letter read. "Our legal center includes a network of cooperating attorneys from around the country, including Indiana, and we have litigated constitutional cases in state and federal courts from coast to coast."

It all started last year on the first day of school.

Duane Nickell, a physics teacher, was just about to turn on the day's announcements, which include the Pledge of Allegiance. It was then, Nickell said, that he told his class of 25 or so students that they were not required to recite the pledge.

Several Supreme Court cases have upheld the notion that schools cannot force students to stand for or recite the pledge.

"I just wanted them to feel comfortable if they didn’t want to say it," he said. "That’s OK with me."

Nickell identifies as an atheist and has clashed with the school administration over the years over what he calls "philosophical differences." In November, with the help of the ACLU, Nickell filed a lawsuit against Franklin Township Community Schools over the school board's use of prayer at its meetings.

Nickell says he personally doesn't recite the pledge, but never tried to talk students out of saying it themselves.

"I did not use that occasion to expound on my personal opinions on the pledge," Nickell said. "All I said was that it's voluntary."

About a week later, though, Nickell said he was called into Principal Kevin Koers' office.

"It's the same way with the teachers as the students," Nickell said. "If you get called to the principal's office ... that means you're in trouble."

Nickell said he brought a representative from the Indiana State Teachers Association to the meeting with him. The vice principal also was present, he said.

At the meeting, Nickell said Koers told him several parents had called to complain about Nickell's guidance on the Pledge of Allegiance.

"His statement to me was that it was not my place to say that," he said. "He said it was the parent or student's place."

Neither Koers, nor administrators for Franklin Township Schools responded to IndyStar's requests for comment. Representatives from AHA's legal center said they have not received a response from the school, either.

Nickell said he doesn't disagree that it's up to parents and students to decide whether to participate in the pledge, but he stands by his decision to inform them of their right to opt out.

"If they don't know they have a choice, how can they make a choice?" Nickell asked.

Nickell said he didn't discuss the pledge in his classes again and the issue did not resurface during the year. Still, the interaction troubled him.

Nickell said he reached out to the AHA then, after finding the organization online. They offered to send a letter, but Nickell asked them to wait. He was afraid of losing his job.

After retiring at the end of the school year, Nickell got back in touch with the group.

"Even after a year, I just find it outrageous that a school principal doesn't want the students to know their rights," he said.

According to a news release from the group, it has been sponsoring a boycott of the Pledge of Allegiance to protest the insertion of the words “under God,” into the recitation. Those words were added in 1954, during the Cold War, after lobbying by religious groups. Humanists and others see the language as a divisive violation of church-state separation principles.

“Restricting the flow of information is a disservice to the schoolchildren and an insult to the Pledge itself,” David Niose, Legal Director for the Appignani Humanist Legal Center, said in the release. “It’s unfortunate that educators would choose to suppress knowledge rather than enlighten students.”

Call IndyStar reporter Arika Herron at (317) 444-6077. Follow her on Twitter: @ArikaHerron.