(JTA) — Just before classes started in September, the teachers union at Barrack Hebrew Academy in Bryn Mawr, Pa., successfully negotiated a new contract with the administration.

Five years earlier the pluralistic middle and high school’s teachers had gone on strike, forming a picket line outside the school after contract negotiations broke down. But since then, the school board and faculty have been meeting monthly to smooth relations, and union leaders report that the administration negotiated the current contract in good faith.

But with its strong union, Barrack is an outlier among American Jewish day schools. Unions exist in only a handful of schools, all of them Conservative movement-affiliated or pluralistic, and the number is dropping.

Over the past year, three Conservative Jewish day schools have effectively eliminated their teachers unions. Perelman Jewish Day School, an elementary school just a few miles away from Barrack, and the Solomon Schechter School of Greater Boston have both declined to negotiate with their teachers unions. According to one source, a third East Coast Conservative day school has done the same, but the source asked JTA not to name the school for fear of disrupting efforts to reverse the policy.

In 2005, the Hillel Day School of Greater Detroit successfully shut down its union. And several people involved in the matter said that eliminating the union was one factor in the 2012 closing of the Reuben Gittelman Hebrew Day School in New York’s Rockland County. A new and non-unionized school, Rockland Jewish Academy, opened just months later with many of the same board members and faculty.

The moves come as public school teachers unions are increasingly finding themselves on the defensive, often portrayed by reformers as obstacles to innovation and as putting the needs of teachers before students. Jewish schools have many of the same concerns in dealing with their unions, but their hand has has been strengthened by the reluctance of the National Labor Relations Board, which enforces national labor laws, to intervene.

In August, in a move that could have implications for all parochial school teachers unions, the Philadelphia office of the NLRB dismissed a complaint from Perelman’s teachers, saying it lacked jurisdiction because the school is a religious institution. The union has appealed the decision to the board’s Washington headquarters.

Dennis Walsh, the board’s Philadelphia regional director, told JTA that while not all religious institutions are automatically exempt from the National Labor Relations Act, many are, adding that there is a complicated set of criteria that the national agency is “in the process of reconsidering.”

Leaders of recently de-unionized schools declined JTA’s requests for interviews about the labor issue. Pro-union teachers say the moves have hurt morale and created a climate of fear.

“People are kind of worried,” said a longtime Boston Schechter teacher who asked not to be identified for fear of retribution. “The new handbook says people can be let go at any time with no notice. It’s very stark language. They’ve done a good job of making people look over their shoulders.”

Anti-union efforts in the public school world are often portrayed as initiatives to improve educational outcomes, allowing school districts to eliminate ineffective teachers who under many union contracts are difficult to fire.

Flexibility in hiring and firing is also an issue at Jewish day schools, but according to Harry Bloom, the strategy manager for financial sustainability at the Partnership for Excellence in Jewish Education, the current pressure on unions is driven by economics. Since 1998, the number of Schechter schools in the United States has dropped from 63 to 39 and the number of students has shrunk 45 percent, to 9,700 from 17,700, according to data from the Avi Chai Foundation.

“Those schools are now half their previous size and people are struggling to pay tuition after the recession,” Bloom said. “What happened is that work rules and staffing and benefits that used to be affordable when you had a school of 1,000 students is now hard to support when you have a school half that size or less.”

That all the schools enmeshed in recent labor conflicts are affiliated with the Conservative movement (Detroit’s Hillel was a Schechter school in 2005, but later became a community school) has not escaped the notice of Jill Jacobs, a Conservative rabbi who authored the Conservative Rabbinical Assembly’s 2008 legal ruling supporting the right of workers to unionize. The R.A.’s Committee on Jewish Law and Standards approved the ruling by a vote of 13 to 1, with three abstentions.

“I think halachah is extremely clear on this point that you’re not allowed to bust a union,” said Jacobs, the executive director of T’ruah, formerly Rabbis for Human Rights of North America, adding that when it comes to labor laws, Jewish institutions should “be doing more than the law requires.”

Leaders of the Schechter Network, which represents Conservative day schools, and RAVSAK, which represents community schools, declined to comment on recent labor conflicts.

Jon Mitzmacher, executive director of the Schechter Day School Network, referred JTA to an Aug. 29 blog post that takes no position on unions while noting that “genuine debate has broken out within the Jewish community (as in the larger American community) about the balance between protecting the rights of teachers and serving the needs of students.”

Marc Kramer, RAVSAK’s executive director, said in an email that the network has no position on teachers unions.

“We obviously want schools to be in the best position possible to stay student focused and to retain the best educators possible,” Kramer said. “Likewise, we believe that day school educators are professionals who should be treated as such … and we do not think that these two commitments need to be in opposition to one another.”