The blow the U.S. Supreme Court dealt public-employee unions Wednesday was met with so much alarm in some quarters that many Americans are likely to conclude that it was a knockout punch. It is not — at least not in the near term.

But the high court’s decision in Janus vs. AFSCME Council 31 is clearly a turning point, both for public-sector unions and the larger American labor movement. What they do in response will determine whether they wind up “smaller and poorer,” as one analyst predicted, or learn to thrive without being able to compel “agency fee” payments from workers who refuse to join their bargaining unit’s union.

Those payments — 78 percent of dues in plaintiff Mark Janus’s case, 85 percent in the case of Minnesota state employees — were outlawed by the 5-4 decision written by Justice Samuel Alito. He wrote that compelling any payment to a union by a nonmember violates that individual’s First Amendment guarantees of freedom of speech and association. Alito dismissed union objections to allowing “free riders” to enjoy union-negotiated benefits without paying dues as “not a compelling state interest” of the kind needed to override a constitutional right.

Maybe it is not. But the ability to collect payments from represented workers has been a compelling union interest since the movement’s inception. And that movement in turn has been a major force in enlarging the American middle class and securing a better quality of life for all working people. Not coincidentally, we’d claim, nonunion American workers’ pay lagged that of unionized workers by 20 percent last year, federal data show. We’re loath to see unions disappear.

Where unions are absent, dissatisfied workers have increasingly looked to governments to set labor standards. The result — as seen recently in the city of Minneapolis — can be ham-handed, one-size-fits-all approaches that cause significant hardship in some industries. The terms of employment are better set at the bargaining table than at City Hall.

That said, we’re among the Americans who have had qualms about the clout public-employee unions have gained since a 1977 Supreme Court decision allowed them to compel nonmembers to pay agency fees — a decision that Wednesday’s ruling reverses.

Public employees now comprise nearly half of the nation’s unionized workers, the U.S. Bureau of Labor Statistics reported earlier this year. They are positioned to, in effect, bargain twice, once during contract negotiations and again during legislative and congressional budget-­setting sessions as they press their political allies for more government spending. Their prominence within the Democratic Party has made them objects of suspicion among Republicans.

The Janus ruling should be heard in both public and private union halls not as a death knell, but as a call to action and reform. It’s a summons to sell a new generation on the value of collective bargaining. It’s a challenge to adapt union practices to the work patterns and emerging industries of the 21st century. It’s a demand to curb the excesses that have turned off otherwise-sympathetic Americans. Union zeal for defending poor employee performance is one such excess. Large financial contributions that flow exclusively to one political party are another.

Last year saw a small uptick in private-sector union membership in America and an overall gain of 262,000 union members. We’ll take that as a sign that this nation’s unions still have some life in them. We hope there’s vitality enough for meeting the challenge that the Janus ruling has handed them.