New York public-sector unions could lose 200,000 or more members in the wake of Wednesday’s U.S. Supreme Court ruling on collective bargaining, though a law the state adopted in March could blunt the impact by making it harder for people to opt out of union representation.

Further, the potential reduction in members could reduce the political influence of unions — which arguably have been the single-most influential special-interest group in New York for years. Union members counter the outcome of the so-called Janus case and subsequent threat to membership will “galvanize” the labor movement.

By a 5-4 decision, the Supreme Court struck down a 1977 law forcing  nonunion members to pay fees to the union representing them in collective bargaining. The court said the mandate violated the First Amendment rights of Mark Janus, the Illinois state worker who brought the lawsuit. Unions had argued nonmembers were benefiting from collective bargaining, legal representation and other perks of membership.

The outcome could have multiple consequences in New York, the most heavily unionized state in the nation.

Here, some 200,000 public employees pay union dues though they aren’t union members, according to the Empire Center, a conservative-leaning think tank in Albany. That is out of more than 1 million total public-employee union members. In theory, the non-members could soon quit paying dues, costing the unions millions of dollars. The unions currently collect more than $800 million annually in dues and fees.

And current union members could opt out, too, further reducing organized labor’s ranks.

When Michigan dropped mandated fees, public-employee membership dropped roughly 25 percent. Professional and civil-service unions saw the steepest decline while police, fire and corrections saw very little, according to the Empire Center and other reports.

Anticipating the Janus decision, Gov. Andrew M. Cuomo and state legislators approved a law in March to blunt some of the impact. Though it includes other aspects, the law most importantly allows unions to control and limit the time period for opting out of membership.