LAS VEGAS — Four of the country's biggest unions are seeking to position themselves as kingmakers in the event of a contested presidential nomination battle, maneuvering to get their members elected as delegates who would throw their weight behind labor's preferred candidate at the Democratic National Convention.

The recent narrowing of the Democratic field essentially to former vice president Joe Biden and Sen. Bernie Sanders (I-Vt.) may reduce the chances of a fight in July in Milwaukee. But the primary season has repeatedly changed course and confounded expectations, and the unions, which have been courted by both leaders, want to ensure they have influence regardless.

The four unions involved in the effort are likely to control at least 7 percent of the delegates at the convention and perhaps more, giving them significant clout if the vote goes to a second ballot and delegates are no longer bound to a particular candidate.

“I’m trying to get away from ‘this is another smoked-filled room’ — it’s not that,” said Randi Weingarten, president of the American Federation of Teachers, one of the unions involved in the push. “By having people who are like-minded, you end up having on the convention floor people who actually can help get to a candidate who could be embraced by the country.”

Democratic delegates are generally elected in state primaries, caucuses or conventions. The unions are actively helping their members navigate that process, which means anything from connecting members with the right presidential campaign to helping them mount their own campaigns for delegate. Some unions are also offering financial incentives for their members to attend, providing hotels and airfare to defray the costs of the Milwaukee convention.

In 2016, the four major service unions accounted for roughly 615 delegates, but this year they have vastly increased their efforts, recruiting delegates earlier and more aggressively.

The National Education Association, the country’s biggest teachers union, already has 100 delegates heading to the convention and at least 1,500 more expressing interest, according to the union. The American Federation of State, County and Municipal Employees is making a similar push.

“As soon as people started talking about the possibility of a second ballot . . . I knew it was going to take organization and talking with people and communicating with them and bringing them into the process,” said ­AFSCME President Lee Saunders. “Our union will have a lot of sway.”

The Service Employees International Union is also involved in the effort, leaders of the other unions say. Asked for comment, SEIU officials did not directly address the delegate push.

“Right now, SEIU members are laser-focused on electing candidates up and down the ballot who will move power away from corporations and back towards working people,” said SEIU spokeswoman Sara Lonardo, adding that SEIU members “when the time comes look forward to participating in the convention process.”

Most unions so far have not endorsed, worried about a repeat of 2016 when many came out early for Hillary Clinton and alienated members who supported Sanders. If Democrats are divided at the national convention, union leaders could seek to extract promises from candidates in exchange for their support.

A messy convention could turn off voters, many Democrats fear, as the chaotic Chicago one infamously did in 1968. But major figures — including former presidents Barack Obama and Bill Clinton and the party’s last presidential nominee, Hillary Clinton — have so far shown little inclination to intervene on behalf of any candidate.

The labor movement sees itself as potentially filling that kingmaker role.

Old-line industrial unions have lost clout, but service unions, often more diverse and liberal, have been energized in recent years. Unions saw a 250 percent increase in strikes in 2019 compared with 2017, according to the Bureau of Labor Statistics. Last year, teachers in at least 18 states registered some kind of protest, including strikes and rallies, according to the NEA.

Rather than embracing a particular contender, many unions are urging their members to become delegates for whichever candidate they prefer, with the hope that if there are multiple ballots the unions will find a way to unify behind one candidate.

“We’ve never been this intentional. We’ve never been this organized,” said Lily Eskelsen García, president of the 3 million-member NEA. “And this is where you can make a difference, because nobody knows what’s going to happen at the convention.”

García said it will be crucial for unions to coalesce around one standard-bearer.

“In general, whether it is this convention or any other convention, unity is a good thing — I don’t think that’s blowing anybody’s secret plan for world domination,” she said. “When you’re unified, you win.”

The delegate push was on full display last month in Las Vegas, when AFSCME leaders hosted an intimate forum on the eve of the Nevada caucuses at Doña Maria Tamales restaurant for members to hear from presidential candidates or their surrogates.

After two hours of grilling candidates, AFSCME’s Saunders urged his members to take two actions: Attend a caucus and sign up to become a delegate.

“If you have an interest in continuing — and continuing to make a determination on who will be the next president of the United States — run for delegate,” Saunders told the roughly 35 union members. “You can see us all in Milwaukee, because it could be a very, very charged convention.”

As the forum ended, union staffers fanned out, promising members AFSCME would provide free transportation to Wisconsin and take care of hotel costs. They also made it clear that members at the convention would be expected to stay in close touch with AFSCME leaders, attending strategy sessions aimed at uniting the delegates.

The NEA is also recruiting heavily. This year, for the first time, an entire section of its website is dedicated to helping members become delegates. “In a contested convention, delegates have major power,” the site’s “Delegates 101” page exhorts.

“You could end up picking the party’s nominee,” it explains. “If nobody wins in the first ballot, delegates are free to shift their votes to the (pro-education) candidate of their choice.”

Senior NEA staffers scoured through rules manuals from all 50 states and the territories, condensing the process to a one-page summary for each. The website outlines how to become a delegate in each state — noting that in Connecticut, for example, many delegates are elected at a post-primary caucus on May 27.

In interviews, union leaders are quick to say they do not have absolute power over their members at the convention.

“I have to make a case to those folks, whether that comes at the convention or whether that comes before the convention,” García said. “They aren’t just going to do it because I said so.”

Still, union officials are confident they will have considerable leverage.

“It’s not like the 1950s when you pick up a phone and bark and order,” said Eddie Vale, a labor strategist familiar with the plans. “But it’s a safe bet that they will be highly influential.”

Democratic insiders agree, noting that labor leaders have always found ways of influencing what their delegates do.

“Who would want to be seen as voting against their union?” said Elaine Kamarck, a member of the Democratic National Committee who has written a book on primaries.

Beyond that, union members who put in the effort to become delegates typically have some ambition to rise within their local labor organizations, giving them an incentive not to break off from a concerted unity effort and go their own way.

Saunders said the service unions have worked together at previous Democratic conventions. But if the convention is in any sense up for grabs, their efforts could be vastly more significant this time.

“We have brought our delegates together and talked about the issues,” Saunders said. “They’re talking about, ‘Okay, what’s the strategy? What’s our message? What should we be doing? What should we be pushing?’ And it’s going to be coordinated. . . . That’s very, very effective and very powerful.”

Some union staffers noted wryly that the scenario of labor swaying a convention was explored in popular culture via a story arc in NBC’s “The West Wing,” a drama that aired on NBC from 1999 to 2006.

In the sixth season of the series, the Democratic Party struggles to settle on a nominee to succeed President Josiah Bartlet, and a leading contender looks to a fictional teachers union to find delegates who would switch their allegiance and provide the votes needed to clinch the nomination.

Asked about the show, Weingarten, who heads one of the country’s real teachers unions, simply said, “I know, I know.”