URBANA, Ill. -- The University of Illinois has fired an adjunct professor who taught courses on Catholicism after a student accused the instructor of engaging in hate speech by saying he agrees with the church's teaching that homosexual sex is immoral.

The professor, Ken Howell of Champaign, said his firing violates his academic freedom. He also lost his job at an on-campus Catholic center.

Howell, who taught Introduction to Catholicism and Modern Catholic Thought, says he was fired at the end of the spring semester after sending an e-mail explaining some Catholic beliefs to his students preparing for an exam.

"Natural Moral Law says that Morality must be a response to REALITY," he wrote in the e-mail. "In other words, sexual acts are only appropriate for people who are complementary, not the same."

An unidentified student sent an e-mail to religion department head Robert McKim on May 13, calling Howell's e-mail "hate speech." The student claimed to be a friend of the offended student. The writer said in the e-mail that his friend wanted to remain anonymous.

"Teaching a student about the tenets of a religion is one thing," the student wrote. "Declaring that homosexual acts violate the natural laws of man is another."

Howell said he was teaching his students about the Catholic understanding of natural moral law.

"My responsibility on teaching a class on Catholicism is to teach what the Catholic Church teaches," Howell said in an interview with The News-Gazette in Champaign. "I have always made it very, very clear to my students they are never required to believe what I'm teaching and they'll never be judged on that."

Howell also said he makes clear to his students that he's Catholic and that he believes the church views that he teaches.

McKim referred questions to university spokeswoman Robin Kaler, who said she couldn't comment on Howell or his firing because it's a personnel issue.

According to the university's Academic Staff Handbook, faculty "are entitled to freedom in the classroom in developing and discussing according to their areas of competence the subjects that they are assigned."

In an e-mail to other school staff, Ann Mester, an associate dean at the College of Liberal Arts and Sciences, said Howell's e-mail justified his firing.

"The e-mails sent by Dr. Howell violate university standards of inclusivity, which would then entitle us to have him discontinue his teaching arrangement with us," Mester wrote.

Cary Nelson, president of the American Association of University Professors, said professors should be able to tell students their own views and even argue in favor of them, provided students can disagree without being penalized.

"It's part of intellectual life to advocate for points of view," said Nelson, an emeritus English professor at the University of Illinois. "Hopefully when they go out in the world, they can emulate that. They can argue a case, and do it in a well-informed and articulate way, and can make a more productive contribution to our democracy that way."

Howell has taught at the university for nine years, and was recognized by his department in 2008 and 2009 for being rated an excellent teacher by students.

He said he and McKim disagree on religious views and believes he lost his job over "just a very, very deep disagreement about the nature of what should be taught and what should not be taught."

After he lost his teaching job, Howell also was fired as director of the St. John's Catholic Newman Center's Institute of Catholic Thought. The on-campus center directed questions to the Diocese of Peoria, which had paid for his position.

Patricia Gibson, an attorney and chancellor of the diocese, said Howell was let go because he could no longer teach at the university.

"We are very concerned and very distressed by what we understand is the situation from Dr. Howell," she said. The diocese hopes to discuss the situation with someone at the university, she said.

A Christian legal defense group, The Alliance Defense Fund, said it is considering helping Howell.