One of the country’s most aggressive unions is slashing spending as it braces for a Trump administration it says will be hostile to organized labor.

The Service Employees International Union will reduce its $300 million budget 30 percent over the course of next year, including a 10 percent cut next month. The union, which represents 2 million health care, janitorial, and other service workers, has spent heavily to organize fast-food and other low-wage jobs, scoring several recent contract victories in Massachusetts.

“Because the far right will control all three branches of the federal government, we will face serious threats to the ability of working people to join together in unions,’’ Mary Kay Henry, the union’s president, wrote in a Dec. 14 memo to staff. “These threats require us to make tough decisions that allow us to resist these attacks and to fight forward despite dramatically reduced resources.’’

Specifics of the cutbacks were not included in the memo, which was first reported by Bloomberg. The SEIU on Tuesday did not respond to questions seeking details.

While Donald Trump won a higher percentage of union votes than previous Republican presidential candidates, there is deep concern among some labor leaders that he will make it more difficult to organize workers and collect dues. The SEIU’s move may be a harbinger of more widespread union belt-tightening.

“The fact that [the SEIU is] cutting their budget means that the American labor movement is licking its wounds with the election of Donald Trump, said Gary Chaison, a professor of industrial relations at Clark University in Worcester. “It means they have to devote more money toward politics and influencing political actors and considerably less money to organizing and growing.’’

Trump’s judicial appointees in particular could weaken unions by limiting a key source of funding. After Supreme Court Justice Antonin Scalia’s death, the court deadlocked 4-4 on a case that could have allowed public sector workers to refuse to pay union dues, but several similar cases are making their way through the lower courts. Several states have similar “Right to Work’’ laws for private sector employees, and labor unions worry that a federal law could be on the table.

The SEIU has been at the forefront of the push for a national $15-an-hour minimum wage, and its retrenchment could slow that campaign. The effort has brought renewed attention to raising wages, leading a number of businesses and cities, and the state of California, to raise their minimum pay to $15 an hour. But it has also cost the union tens of millions of dollars to support workers who don’t yet pay dues.

It’s unclear what SEIU’s move will mean for Massachusetts, where the international union supports upcoming legislation to increase the state’s minimum hourly wage to $15, But Massachusetts is in a better position than many other states, said Harris Gruman, the Massachusetts political director for SEIU, and the legislative effort will go on regardless.

“In Massachusetts we have a broad movement that will carry the fight forward,’’ he said. “It has a life of its own that it didn’t have when we started.’’

The SEIU cuts won’t change 32BJ SEIU District 615’s plan to scale up its organizing efforts, including more emphasis on strikes, said Roxana Rivera, who heads up the union that is working to organize workers at Logan Airport. “These will be challenging times,’’ she said, via e-mail, “but this is more important than ever and we won’t back down.’’

This past fall, Rivera negotiated three contracts for local janitors, raising wages to between $20 and $25 an hour.

The SEIU’s spending reductions are concerning, said Jim Carvalho, spokesman for the United Food and Commercial Workers International Union Local 1445, which counts Stop & Shop workers among its members. But he doesn’t anticipate drastic actions locally.

“Not knowing what’s going to happen, we obviously are going to be more cautious with our budgets, but not change anything drastically,’’ he said.

Steven Tolman, president of the Massachusetts AFL-CIO, said he was not aware of other unions making reductions but was not surprised by the SEIU’s decision given the probability that the courts could “cut out the money supply.’’

“There are going to be financial hits,’’ he said, “but it means we have to work smarter and be more organized because our challenges are going to be bigger.’’

Katie Johnston can be reached at katie.johnston@globe.com. Follow her on Twitter @ktkjohnston.