The Justices decided in a 5-4 ruling on Monday to not overturn a 37-year precedent that allows public unions to collect dues from non-members. But the nation’s top court did recognize a category of “partial public employees” that cannot be forced to contribute union fees, which will limit unions’ ability to represent a fast-growing pool of potential members: home care aides.

The decision had the potential to be a death knell for unions, which are already struggling to maintain membership rolls. Union membership in the U.S. stands at 11.3%, down from 20.1% in 1983, according to the Bureau of Labor Statistics. The one relatively healthy sector for unions—the public sphere, where 35.3% of the workforce is unionized—was put at serious risk in the case decided Monday.

The case grew out of a law passed in Illinois in 2003 that recognized some home care providers as public employees and selected a Midwest branch of the SEIU to exclusively represent these workers.

The law held that no home care workers would be compelled to join the SEIU but that all workers would be required to contribute “fair share” dues to the union since the law directed the SEIU to collectively bargain on behalf of all the workers covered by the law regardless of whether the workers wanted the representation.

The Illinois law relied a 1977 decision by the Supreme Court in Abood v. Detroit Board of Education that said that states could require employees to pay partial union dues to cover the cost of unions bargaining on their behalf.

The lead plaintiff in the case, Pamela Harris, worked as a home care aid and was represented by the conservative National Right to Work Legal Defense Foundation, which aimed to upset the Illinois law and the Abood decision with a class action suit. Harris claimed that Illinois was infringing on her first amendment rights since the money that the SEIU automatically subtracted from her paycheck constituted compelled speech in support of the union.

Unions, meanwhile, argued that the required dues prevents freeloaders—those who enjoy the benefits of union representation without having to pay for it.

“This case represents a very, very aggressive attempt by the National Right to Work Foundation to try to make America a right-to-work country in which public unions can never compel dues from people,” Lee Adler of Cornell’s Industrial and Labor Relations School told Fortune. And history has shown that many workers choose to avoid paying union dues if they are given the option, meaning that a decision overturning Abood could have crippled public unions.

But those fears weren’t wholly realized on Monday. In writing for the majority and siding with the home care aides, Justice Samuel Alito, a conservative, kept Abood in place while ruling that personal home-care employees couldn’t be forced to pay union dues because they are not technically full-time state employees. “Abood involved full-fledged public employees, but in this case, the status of personal assistants is much different,” Justice Alito said in his opinion.

While the decision didn’t mark as big a blow to unions as it could have, it has hit labor where it hurts. Personal care aides help elderly or disabled clients with everyday tasks and are paid through Medicaid. It’s a low paid profession—about $20,000 annually—that’s expected to grow by 580,000 workers by 2022 as the nation’s population ages, according to the BLS. The field is ripe for unionization and labor has tried—and succeeded—to organize workers in several states.

“Other states have decided like Illinois to share the control over the workers, so this decision has the potential to impact those other programs,” says Cathy Ruckelshaus, general counsel for the National Employment Law Project. A decision against the unionization of these workers will trickle through the elderly and disabled care system, which already has a shortage for workers since working conditions are so poor. “It’s a blow not just to the individual workers,” she said, “but also to the care and service provided to the recipients.”