WASHINGTON—A Supreme Court ruling last week that says a religious school can claim a “ministerial exception” to a discrimination charge under the Americans with Disabilities Act for a teacher who also taught secular subjects will discourage litigation in this area, say many observers.

But the court's unanimous Jan. 11 decision in Hosanna-Tabor Evangelical Lutheran Church and School vs. Equal Employment Opportunity Commission et al., does not make clear the extent to which the ministerial exception applies to other religious-organization employees, say some observers.

The nation's highest court also said the ministerial exception bars only employment discrimination lawsuits.

“We express no view on whether the exception bars other types of suits, including actions by employees alleging breach of contract or tortious conduct by their religious employers,” Justice John Roberts wrote for the court.

Most attorneys say the Supreme Court ruling will result in fewer lawsuits by employees of religious institutions.

The ruling concerns Cheryl Perich, who worked as a “called teacher.” Called teachers have satisfied certain academic requirements and “are regarded as having been called to their vocation by God through a congregation,” according to the opinion. In addition to teaching, she was designated a commissioned minister after completing certain academic requirements, including a course of theological study. In addition to teaching secular subjects, she taught a religion class, led her students in daily prayer and devotional exercises, and took her students to a weekly chapel service for the entire school.

Ms. Perich was terminated in 2005 after the school refused to reinstate her after a disability leave, although a doctor said she could return to work with no restrictions. She then filed suit, claiming discrimination and retaliation under the ADA.

A lower court agreed with the school that it was entitled to a “ministerial exception” to the ADA and dismissed the case.

However, in its unanimous opinion in 2010, the 6th U.S. Circuit Court of Appeals in Cincinnati disagreed, stating that “legislative history makes clear that Congress intended the ADA to broadly protect employees of religious entities from retaliation on the job, subject only to narrowly drawn religious exemption.” Ms. Perich's participation in some religious activities “does not make her primary function religious,” the appeals court said.

In overturning the appeals court, the Supreme Court said that while it has not ruled on this issue until now, it agrees with appeals court rulings that there is a ministerial exception grounded in the First Amendment.

“The members of a religious group put their faith in the hands of their ministers. Requiring a church to accept or retain an unwanted minister, or punishing a church for failing to do so, intrudes upon more than a mere employment decision. Such action interferes with the internal governance of the church, depriving the church of control over the selection of those who will personify its beliefs,” the high court ruled.

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The ministerial exception applies in this case based on “the formal title given Perich by the church, the substance reflected in that title, her own use of that title and the important religious functions she performed for the church,” the court ruled. “We conclude that Perich was a minister covered by the ministerial exception.”

“When a minister who has been fired sues her church alleging that her termination was discriminatory, the First Amendment has struck the balance for us. The church must be free to choose those who will guide it on its way,” the court ruled.

Douglas Laycock, professor of constitutional law at the University of Virginia in Charlottesville, Va., who represented the church in the case, said the ruling “will considerably reduce the litigation in this area.” People “who are clearly ministers will no longer file lawsuits,” he said.

Gerald L. Maatman Jr., a partner with Seyfarth Shaw L.L.P. in Chicago, characterized the opinion as a “courthouse door closer”—meaning that the ruling will make it more difficult for church employees to find counsel to litigate their cases—”because the ministerial exception is given a very broad reading. And given the circumstances and facts in this case, it seems difficult for anyone to get around the ministerial exception, practically speaking,” said Mr. Maatman, who was not involved in the case.

Nathan Adams, a partner with Holland & Knight L.L.P. in Tallahassee, Fla., said the decision provides an “affirmative defense to claims by individuals held out to be ministers, and so to that extent it is likely to be an additional ground” to have their cases dismissed at an early stage.

Plaintiff attorney Paul W. Mollica, of counsel at Outten & Golden L.L.P. in Chicago, said if you go back to the case law on this, it has been recognized since the 1960s that religious school teachers, for example, tend to have the ministerial exemption “because they have a pedagogical mission of promoting the religious space.

“Now, if were talking about somebody who was in the office, a secretary, or somebody who was not involved in teaching students, you might be talking about another issue altogether,” Mr. Mollica said.

Jeffrey A. Pasek, a defense attorney with Cozen O'Connor P.C. in Philadelphia, said the opinion did leave “open how far religious organizations can go in the future in defining categories of employees who are "ministers.'”

In this case, Mr. Pasek said the plaintiff was a “called teacher” who performed the same duties as lay teachers. “It's not clear whether the court's decision would extend” to the lay teachers as well, he said.