After four years under Joe Biden, who enthusiastically called himself “the most pro-union president in American history,” employers and labor groups alike are heading into President-elect Donald Trump’s second term unsure of what lies ahead.

Although his nominee for Labor secretary has won bipartisan praise and has a pro-labor track record, Trump’s threats to deport millions, impose tariffs and weaken worker protections have left many in the labor movement wary of what his time in office will bring.

Here’s what a second Trump administration could mean for labor.

What is the National Labor Relations Board and what could happen to it under Trump?

The National Labor Relations Board is the federal agency tasked with safeguarding the right of private employees to unionize or organize in other ways to improve their working conditions. Under Jennifer Abruzzo, whom Biden appointed to run the NLRB as its general counsel, the board took “a fairly innovative and aggressive approach” to enforcing protections, said labor attorney Benjamin Dictor, who represents several unions, including United Auto Workers and a Teamsters local.

Abruzzo took an expansive approach to labor law that favored workers. For example, she pushed through a ban on noncompete agreements, which restrict a person’s ability to get a new job after leaving a post. She also drove regional offices to pursue more broad remedies for harmed workers and successfully sought a ban on captive audience meetings, in which employers require staff to listen to anti-union arguments.

Dictor and others anticipate the Trump administration will swiftly replace Abruzzo with a more employer-friendly general counsel. This type of ping-ponging of priorities from administration to administration is typical, but the change is expected to be even more pronounced, given Abruzzo’s novel approach.

Trump also has a clear path toward securing a Republican majority on the five-member board itself, which will allow his administration to reverse gains that unions made under Biden. The labor board probably will seek to reverse decisions that expedited the union election process, put pressure on employers to voluntarily recognize and negotiate with unions, prohibited confidentiality and non-disparagement provisions and banned captive audience meetings, among other actions, said Adam Primm, an attorney who represents employers.

Senate Majority Leader Charles E. Schumer (D-N.Y.) led a last-ditch attempt last week to lock in Democratic control of the board for the next two years, but the effort collapsed when the Senate failed to approve a second term for one of Biden’s nominees.

Trump has promised to deport millions of people. What would that mean for the economy?

A major deportation effort could have a significant effect on industries that rely heavily on immigrant workers including agriculture, construction and hospitality.

The Center for Migration Studies of New York estimates that as many as 8.3 million immigrants working in the U.S. are here illegally and they represent more than 5% of the workforce.

Among employers there is rising concern that under Trump there will be a significant increase in workplace raids, audits of employment eligibility documents and other immigration enforcement actions against companies, said George Howard, an attorney with Quarles & Brady.

Labor advocates, meanwhile, worry about the opposite happening: Enforcement against unscrupulous employers will fall by the wayside.

For example, immigrant labor advocates expect Trump will do away with a Biden program that awards job permits to undocumented workers at companies under investigation for workplace violations — an effort intended to encourage cooperation with investigations of safety, wage and other labor violations.

Attorney Yvonne Medrano of Los Angeles-based Bet Tzedek Legal Services, a nonprofit legal advocacy group, said there is concern that employers of undocumented immigrants may feel emboldened to exploit workers if the government eases up on efforts to root out wage theft, child labor and other violations.

Trump has said he will impose sweeping tariffs. How could they affect American workers?

Trump has said he will impose sweeping tariffs on key trading partners including Canada, Mexico and China as soon as he takes office. The effects of those tariffs could hit American workers in several ways.

Prices would rise on certain goods in industries affected by tariffs, broadly increasing the cost of living and eroding workers’ purchasing power unless wages rise commensurately, said Mark Zandi, chief economist at Moody’s Analytics.

Higher prices would have an outsize effect on lower-income workers because a larger proportion of their budget is spent on food and clothing, Zandi said.

And it’s likely that countries facing tariffs from the U.S. would retaliate with their own tariffs, as China did during Trump’s first term. The trade war Trump led in his first term delivered higher costs to consumers and uncertainty to the U.S. auto, agricultural and manufacturing sectors.

Companies that rely on imported goods, such as machine parts and industrial supplies, will be forced to pay more for those goods, ballooning their costs and potentially forcing them to make job cuts, Zandi said.

Trump has picked Lori Chavez-DeRemer, a pro-union Republican, to lead the Labor Department. What does that mean for workers?

The union-friendly track record of Trump’s Labor secretary choice has fueled anxiety among the GOP, with several Republican senators expressing concern. Lori Chavez-DeRemer is known for being one of only three GOP lawmakers who co-sponsored legislation, known as the PRO Act, that would have significantly expanded labor rights, including measures that increased penalties for employer labor law violations and expanded union eligibility.

Trade groups have also emphasized concern with the choice.

“IFA looks forward to ensuring the job-killing PRO Act and Biden-era joint employer standard have no place in the incoming administration,” Matt Haller, chief executive of the International Franchise Assn., said in a recent statement. He was referring to an attempt by Biden to broaden rules for when two or more companies should be considered employers of a group of workers.

Although a pro-worker appointee has sparked concerns, attorney Patrick Muldowney, who represents employers on labor issues, said the appointment does not mark a tangible threat to employers.

“I don’t see that as moving the needle very far,” Muldowney said.

The Department of Labor administers federal laws governing minimum hourly wage and overtime pay, as well as protection against employment discrimination, workplace safety rules and unemployment insurance. Its reach is less visible in states like California that have implemented stronger protections than those offered at the federal level.

Labor advocates still expect the Trump administration to pursue anti-worker changes under Chavez-DeRemer.

Judy Conti, government affairs director of the National Employment Law Project, said she anticipates the Trump administration will ease up on enforcing safety rules, narrow eligibility for overtime pay and make it harder for gig-economy workers to gain status as employees.

“Chavez-DeRemer’s record suggests she understands the value of policies that strengthen workers’ rights and economic security,” said Rebecca Dixon, president and CEO of NELP, in a news release last month. “But the Trump administration’s agenda is fundamentally at odds with these principles.”

Her “true commitment to workers will be tested,” Dixon said.