A little-known religious exemption to United States labor law may have just become extremely important, thanks to the Supreme Court’s ruling in Hobby Lobby.

By declaring that “closely held” corporations may hold religious beliefs, the court may have provided businesses with a new tool for crushing workplace unionization drives. In addition to declaring themselves exempt from contraception mandates and non-discrimination laws, religious employers may soon be able to argue for an exemption from collective bargaining laws.

“All you need is one employer saying, ‘My religious beliefs tell me I shouldn’t collectively bargain,’” said Alex Luchenitser, associate legal director for Americans United for Separation of Church and State. If an employer takes the National Labor Relations Board (NLRB) to court and uses that argument, it could set the table for a major court battle over the future of union rights in nominally religious workplaces.

Religious primary and secondary schools are already exempt from collective bargaining rules, thanks to the 1979 Supreme Court case NLRB v. Catholic Bishop of Chicago. In a 6-3 decision, the court ruled that the NLRB does not have jurisdiction over schools “operated by a church to teach both religious and secular subjects.” As a result, schools operated by the Catholic Bishop of Chicago were under no obligation to recognize employee unions, no matter the circumstances. Putting religious schools under the jurisdiction of the NLRB, the court reasoned, would present “a significant risk of infringement of Religion Clauses of the First Amendment.”

Other religious schools have seized on the decision over the years. Most recently, Perelman Jewish Day School in Philadelphia decided to stop recognizing its teachers’ union, citing NLRB v. Catholic Bishop of Chicago as legal justification. A March 28 article from the labor-friendly magazine In These Times suggested that the school’s actions may have earned it the title “the Hobby Lobby of Union-Busting.” But the Perelman case may wind up being less important than another legal fight brewing elsewhere in Pennsylvania. In 2012, adjunct professors at Pittsburgh’s Duquesne University requested the right to hold a union election, only to have the school claim a religious exemption. The crucial difference in this case is that Duquesne is a university, not a religious day school like Perelman or the Chicago Catholic schools.

“Once you get above the high school level, the organizations tend to have more secular functions as well, or seek to educate people beyond the sort of educating that gets done at the high school level,” said Marcia McCormick, director of St. Louis University Law School’s Center for Employment Law. If a court decides that the NLRB has no authority of Duquesne University, it could expand the NLRB v. Catholic Bishop of Chicago ruling to encompass America’s many religiously-affiliated private universities. The university’s appeal is now pending review by the NLRB’s main office in Washington, D.C.

A similar case is also brewing at Pacific Lutheran University in Tacoma, Wash., where the union SEIU Local 925 is trying to win recognition as the sole bargaining agent for adjunct faculty. The National Right to Work Legal Defense Foundation, which recently defeated organized labor in the Supreme Court case Harris v. Quinn, filed an amicus brief supporting the university’s “efforts to resist union encroachment on its religious prerogatives.”

“If the NLRB recognizes Local 925 as the adjuncts’ exclusive bargaining agent, union officials will be empowered to negotiate over terms and conditions of employment with Pacific Lutheran University,” said the Legal Defense Foundation in a statement. “Those negotiations could force university administrators to make concessions that contradict the school’s religious mission, such as expanding access to abortion under the university’s health care plan.”

If the cases involving Duquesne University and Pacific Lutheran University have the potential to widen the scope of NLRB v. Catholic Bishop of Chicago, a broad reading of the Hobby Lobby decision could stretch it even further. If private corporations can be religious institutions, then private corporations may soon argue in court that they have a First Amendment right to object to collective bargaining on religious grounds.

“Hobby Lobby basically expanded what a potential pool of religious institutions in that sense might be,” said McCormick. She described it as “highly likely” that the Court’s ruling in that case “set the stage for future decisions that will work larger revolutions in the law as we know it.”