INDIANAPOLIS -- An Indiana teacher who says she was fired from a Roman Catholic school for using in vitro fertilization to try to get pregnant is suing in a case that could set up a legal showdown over reproductive and religious rights.

Emily Herx's lawsuit accuses the Diocese of Fort Wayne-South Bend and St. Vincent de Paul school in Fort Wayne of discrimination for her firing last June. Herx, 31, of Hoagland, Ind., says that the church pastor told her she was a "grave, immoral sinner" and that a scandal would erupt if anyone learned she had undergone in vitro fertilization, or IVF.

The Roman Catholic Church shuns IVF, which involves mixing egg and sperm in a laboratory dish and transferring a resulting embryo into the womb. Herx said she was fired despite exemplary performance reviews in her eight years as a language arts teacher.

Legal experts say Herx's case illustrates a murky area in the debate over separation of church and state that even the U.S. Supreme Court has failed to clearly address.

Diocese officials said in a statement issued to The Associated Press on Wednesday that the lawsuit challenges its rights as a religious institution "to make religious based decisions consistent with its religious standards on an impartial basis."

The U.S. Supreme Court ruled unanimously in January that religious workers can't sue their employers for job discrimination because anti-discrimination laws allow for a "ministerial exception." But the justices failed to define who was and who wasn't a religious employee.

"The Supreme Court didn't give us a kind of neat little on-off test as to who's a minister and who isn't," said Rick Garnett, associate dean and professor of law at Notre Dame Law School.

In a similar case in Ohio, a federal judge last month gave the go-ahead for a trial in a lawsuit against the Archdiocese of Cincinnati by a parochial school teacher who was fired after she became pregnant through artificial insemination, which the church is also against. The archdiocese fired Christa Dias in 2010, saying the single woman violated church doctrine.

U.S. District Judge Arthur Spiegel said in his March 29 ruling that the ministerial exception did not apply because Dias was a non-Catholic computer teacher with no role in ministering or teaching Catholic doctrine.