Trump made big gains among blue-collar workers. Is he really on their side?

While campaigning, Trump aggressively courted rank-and-file union members and invited Teamsters President Sean O’Brien to speak at the Republican National Convention in July. At the same time, the former real-estate developer suggested in an interview with Elon Musk, just named to co-head a government efficiency commission, that striking workers should be fired. He recalled at a rally that he “hated to give overtime."

The dissonance reflects a deeper fight over labor policy that is unfolding within the Republican Party. It pits old-guard conservatives who prefer low taxes and minimal government intervention and have generally been hostile to unions, against a self-proclaimed New Right that says it wants to empower workers—and counts Vice President-elect JD Vance among its followers.

People close to the transition said Trump’s potential appointments to key labor positions could include old-guard Republican functionaries, corporate executives, or individuals who are closer to the New Right and see themselves as more pro-worker.

“I think there are some issues where, in the past, a Republican administration would just come in and do the reverse of what the Democratic administration did," such as getting rid of union-friendly government contracts, said Oren Cass, founder of American Compass, a New Right think tank. “I don’t think those things are going to be automatic at all."

But union officials said Trump’s record is at odds with his pro-worker rhetoric. “It’s going to be a rude awakening for a lot of folks who wanted to take Trump at his word," said Steve Smith, a spokesman for the AFL-CIO, which campaigned for President Biden and, subsequently, for Vice President Kamala Harris. “They talk a big game when it comes to workers, but…they’re going to attack the working class."

Karoline Leavitt, a spokeswoman for Trump’s transition, declined to comment specifically on the incoming administration’s plans on several labor issues.

The administration’s most direct impact on the daily lives of 159 million American workers would come through its approach to unions, workplace safety and employee rights.

The National Labor Relations Board oversees how workers form unions and has up to five members plus a general counsel who acts as a prosecutor. It currently has one vacancy, and two members’ terms expire in the next year.

During his first term, Trump appointed former management lawyers to key positions on the NLRB, which according to critics, made a number of decisions that curbed workers’ ability to engage in collective bargaining. Biden reversed that trend: In the 12 months through Sept. 30, the NLRB received double the number of petitions from workers seeking to form a union from the same period three years earlier.

In his first term, Trump’s Labor Department finalized a rule that set the salary threshold at which a worker becomes eligible for overtime pay lower than the level sought by the Obama administration. That difference amounted to eight million fewer people being eligible under the Trump rule, according to Heidi Shierholz, who served as chief economist of President Barack Obama’s Labor Department.

Critics also accused Trump of shrinking the Occupational Safety and Health Administration, which oversees workplace safety and investigates fatalities.

Under Biden, the Labor Department issued rules increasing the number of workers eligible for overtime pay and making it harder for companies to deny workers minimum wage and other protections by classifying them as independent contractors. OSHA proposed rules to protect workers from extreme heat. The Federal Trade Commission banned noncompete agreements for most workers. After the U.S. Chamber of Commerce sued, the rule was overturned in court and faces an uncertain path forward.

Biden calls himself the most pro-union president in history, and several of his executive orders and legislative achievements include language designed to boost union jobs through federal spending. A provision tucked into his 2021 stimulus bill bailed out multiemployer pension plans used by unions such as the Teamsters to the tune of $69 billion.

Harris’s share of union-member votes was slightly higher than Biden’s in 2020, exit polling shows. But the unionized share of the workforce has been in decline for generations, to just 10% in 2023, limiting unions’ election influence.

Trump himself has provided little detail about labor policy beyond his broader plans to restrict immigration and trade, to goose economic activity through tax cuts, and to challenge workplace diversity initiatives. He has also promised to reduce job protections for federal workers. Musk’s SpaceX is challenging the constitutionality of the NLRB’s structure and administrative trials in federal court.

People close to Trump’s transition said they expect the incoming administration to chart a path that aims to help all workers, rather than just union members. It couldn’t be determined whether that will translate into different policies from what Trump and his appointees pursued in his first term.

Project 2025, a proposed transition road map by the conservative Heritage Foundation that Trump has disavowed, calls for restoring “the family-supporting job as the centerpiece of the American economy." The section on labor, written by a former Trump administration labor official, Jonathan Berry, focuses on rescinding progressive cultural priorities related to diversity and LGBTQ protections in the workplace.

A number of Republican lawmakers aligned with Trump, including Vance and Sens. Marco Rubio of Florida and Josh Hawley of Missouri have taken positions that seem to depart from Republicans’ traditional stance toward labor.

All three co-sponsored a bipartisan bill in 2023 aiming to improve safety for railroad workers following the East Palestine, Ohio, train derailment. Rubio—now expected to be Trump’s nominee for secretary of state—backed a unionization push at an Amazon.com warehouse in 2021 and introduced legislation that would ban employers imposing noncompete agreements on low-wage workers. Hawley has said he no longer supports Republicans’ longtime dream of a national right-to-work law that would undermine union influence. That goal no longer appears in the GOP platform.

“These are the kinds of things at least some segments of the Trump coalition are very interested in and seek progress on," said Cass of American Compass. Then, noting Musk’s comments about workers going on strike, he added: “There are also segments that would say this is all terrible."

Write to Paul Kiernan at paul.kiernan@wsj.com