Late last week, the U.S. Supreme Court announced that it will add a case critical to the future of public-sector unions to its docket. With President Donald Trump's appointment of conservative-leaning Justice Neil Gorsuch, many expect the court to rule against the unions.

Such a decision would energize the recent resurgence of state laws that effectively reduce the power of unions in both the public and private sector. Expecting the worst, unions are already preparing for a potential exodus of members and a loss of revenue.

“I’d place a bet that this doesn’t bode well for public-sector unions,” says Patrick Flavin, a political scientist at Baylor University who frequently writes about labor union politics and policy.

The lead plaintiff, Mark Janus, is a child support worker in Illinois who argues his free speech rights are being violated by the requirement that he pay the American Federation of State, County and Municipal Employees (AFSCME), the largest public employee union in the country, even though he chose not to join it and does not support its political views and positions.

Illinois is currently one of 22 states where nonunion members still have to pay so-called agency fees to unions that negotiate on their behalf.

If the Supreme Court rules that making agency fees mandatory is unconstitutional, unions in those states fear the loss of revenue from existing nonunion members and the loss of more members, who could quit unions if granted the right to avoid the paycheck deduction. Such a scenario would weaken unions' bargaining power and their political clout.

“It is an enormously big deal,” says Harvard law professor Benjamin Sachs, who often writes about labor issues. “Unions have to provide services and representation equally to everyone in a bargaining unit. But if you can get those services for free, a lot of people won’t pay them. You have a classic free-rider situation.”

Public-sector union membership has already been on the decline. Between 2000 and 2016, it dropped about 8 percent, to 34.4 percent, according to the U.S. Bureau of Labor Statistics (BLS). Still, that's far greater than in the private sector where only 6.5 percent of employees belonged to a union in 2016, according to the BLS.

The shrinkage of unions can partially be attributed to the recent rise of "right-to-work" laws, which prohibit unions -- private or public sector, depending on the state -- from forcing people to pay dues. Of the 28 states that have passed right-to-work laws, six did it in the last five years. (Most of the rest passed this legislation in the 1940s and 1950s.) In general, the states with the lowest union membership have right-to-work laws.

The right to work is only one of a series of recent attacks on public-sector unions. There have also been ongoing efforts to curtail collective bargaining, which gives unions the right to negotiate with management over wage and other employee-related issues. The passage of Act 10 in Wisconsin in 2011, for example, severely restricted collective bargaining for most state and local government employees. This year, Iowa passed similar legislation, which is now the topic of a union lawsuit.

An anti-union ruling in the Supreme Court case, called Janus v. AFSCME, would mean that all states would, in effect, be right-to-work states for the public sector. In states where collective bargaining is permitted, all employees in a bargaining unit would still be covered by negotiated agreements, but nonmembers wouldn’t have to pay the union for services rendered on their behalf.

While awaiting a decision in the Janus case, unions aren’t sitting quietly on the sidelines. They are already beginning to wage a campaign to persuade employees about the importance of union membership and of the negative consequences of being a "freeloader."

“If unions can convince all their members to continue to pay dues voluntarily, they’ll be able to survive,” says Sachs, the law professor.

Some, however, think the unions will have to do more than that to gain or keep members.

“In order for the public-sector labor movement to recover, they’d have to pretty substantially change the model they’re operating under,” says Alexander Hertel-Fernandez, an assistant professor of international and public affairs at Columbia University. “One strategy is to become much more service-oriented.”

To entice people to stay or join, unions could expand their services to include additional low-cost insurance, counseling services to help with on-the-job stress or training programs to help advance careers. This has already been a strategy in some right-to-work states, says Hertel-Fernandez.

But if an anti-union decision is reached, unions may not have the resources to offer more services. In fact, according to Sachs, they might consider cutting off some of their services to nonmembers -- like refusing to provide help with grievances.

Oral arguments in this case are expected to happen in early 2018, with a decision in the late spring or early summer.