The AFL-CIO, the country’s largest coalition of labor unions, endorsed Joe Biden for president Tuesday, with the organization’s top official vowing to wage an aggressive effort to help him defeat President Trump by reaching out to working-class voters.

Union officials cemented their support for the former vice president in a vote of the organization’s general board, joining a long roster of influential labor groups backing the presumptive Democratic nominee. In an interview with The Washington Post, AFL-CIO President Richard Trumka said his group will be “playing hard” in about a dozen battleground states where it plans to urge members to support his candidacy.

“Joe Biden has demonstrated his character,” said Trumka. “We look forward to helping him get elected president and changing the direction of the country.”

The endorsement highlights Biden’s consolidation of the support of union leaders in the past two months. The larger test, however, is how strongly the recent string of endorsements will motivate union members, some of whom have been drawn to Trump’s message or preferred other candidates to Biden in the primary.

Richard M. “Rick” Gallo, president of the Kenosha County AFL-CIO Central Labor Council in Wisconsin, predicted there will be union members who will support Trump, even if they say otherwise.

“That is the reality. Some of them aren’t going to tell you,” Gallo said. He said on the whole he thinks the vast majority will back Biden but said it was “a little bit concerning” that some remain attracted to pro-Trump rhetoric.

The AFL-CIO, which includes 55 unions representing 12.5 million workers, is a staunch Democratic ally that has been expected to endorse Biden ever since he effectively clinched the nomination. The organization endorsed Hillary Clinton in June 2016.

In 2016, Trump campaigned as a champion of workers, vowing to protect and restore their jobs with staunch opposition to international trade agreements and an anti-immigrant platform.

That message powered him to crucial upsets four years ago in Pennsylvania, Michigan and Wisconsin, home to many white blue-collar voters.

In the 2016 election, 18 percent of voters said someone in their household belonged to a union, according to the national exit poll, and Clinton won those voters by a 51 percent to 42 percent margin over Trump. But her share was smaller than President Barack Obama’s 58 percent support in 2012.

Trump won white voters without college degrees by 64 percent to 28 percent, according to the Pew Research Center. Several recent polls show Trump currently holds a smaller advantage with this group, ranging from 18  to 24 percentage points.

This year, the president has emphasized similar themes, hoping that rank-and-file members will once again flout their leaders’ wishes.

Beyond the states Trump won in 2016, Trumka mentioned Minnesota, New Mexico, Florida and Arizona as among those his group will be targeting. Clinton won the first two, while Trump carried the latter pair.

“We’ll be educating and mobilizing our members,” said Trumka. He said his group would be “talking to them using new methods, to educate them, to get them out to vote, to encourage them to vote by mail.” Trumka did not say how much money the AFL-CIO would spend.

Powerful labor groups largely declined to pick a side earlier this year when the Democratic field was crowded and competitive. As Biden emerged from the pack, they started rallying to his corner. In March, Biden landed the support of the American Federation of County, State and Municipal Employees.

In a statement provided by his campaign, Biden said he was “honored and humbled to have earned the endorsement” and emphasized how the pandemic has upended the lives of workers.

“In the face of COVID-19 we’re seeing without any doubt how important unions are to this country — fighting for their workers to have personal protective equipment, for paid leave, and for safer workplaces,” the statement said, adding, “As we come out of this crisis, there is an incredible need and opportunity to create good-paying, union jobs across the country and ensure the United States owns the 21st Century.”

Organized labor has declined numerically over the years, according to the U.S. Bureau of Labor Statistics, which estimated that in 2019, 10.3 percent of all U.S. workers were union members. In 2010, that figure had been 11.9 percent; in 1983, it was 20.1 percent.

Still, labor remains a strong force in the Democratic Party, as it expands to represent not only white working-class employees but also Latino and African American workers.

Organized labor leaders say they see a critically important role for their groups in this year’s election. “I think the road to the White House goes through the labor movement,” said Trumka.

Democrats are gearing up for a battle over working-class voters in November. They are casting Trump as beholden to the wealthy and powerful and sharply criticizing his response to the coronavirus pandemic, which Trumka said will be a focal point of his group’s efforts.

“Now the president has a record. The record that he has shows that he was willing to do a number of things to hurt workers,” said Trumka, who blamed Trump’s slow response to the virus and subsequent actions for causing harm to the health and economic standing of front-line workers.

Democrats say Biden’s emergence has given them confidence that they will be able to reclaim some key working-class areas they lost to Trump four years ago. Biden has long-standing relationships with unions, has frequently underscored his modest upbringing and Pennsylvania roots, and has long referred to himself as “Middle-Class Joe,” despite accumulating wealth in recent years.

Although Clinton was well-qualified, Trumka said, “30 years of being attacked by the right wing took a toll on her.” Biden, he said, “talks to you like a working person. He comes from working-class people.”

Trump’s campaign disagreed, seeking to draw attention to Biden’s past support for sweeping trade deals.

“Blue-collar workers know President Trump always puts America first, that his policies built the greatest economy in history before it was artificially interrupted by coronavirus, and that he is the only one who can restore us to that position again,” said Trump spokeswoman Erin Perrine. “When faced with the choice of President Trump’s record of accomplishment or Biden’s abysmal record and far-left agenda, the choice for American workers is clear.”

A video released Tuesday showed how union leaders are gently seeking to persuade some Trump voters to switch sides and back Biden.

“Some working people, desperate for a rapid departure from business as usual, took a chance on Trump. Look, I get it. And then, over the past four years, the president showed his true colors,” Trumka says in the video, which touts the Biden endorsement.

Biden has largely been campaigning remotely from his home during the pandemic. He left his neighborhood for the first time Monday to lay a wreath at a nearby veterans memorial. He and his wife, Jill Biden, wore masks during the visit.

Some Democrats have privately expressed anxiety about the former vice president’s strategy, expressing a desire to see him return to the campaign trail in person soon. Trumka said he had confidence in Biden’s approach.

“I think he’s going to comply with all the safety rules and guidelines that have been out,” he said. “He’ll get out to the people.”

Scott Clement contributed to this report.