The senior executive from the nation’s largest labor group walked door-to-door through a middle-class neighborhood in Northern Virginia carrying a twin message for union households.

On Election Day, urged Tefere Gebre, vote not only for Hillary Clinton but also against a proposed amendment to the state constitution that would weaken organized labor.

Standing in a steady drizzle on the stoop of a white house in Woodbridge, Gebre made the sale to postal worker Michael Brown.

“Anything that comes up against unions, I’m voting no,” Brown, 68, assured Gebre. Without unions, Brown said, “it means employers can fire you for no reason at all.”

The involvement of Gebre, ­executive vice president of the AFL-CIO, underlined the high stakes for unions as they try to end a string of political defeats in state elections across the country.

Virginia is one of five states where voters this year will make decisions affecting “right-to-work” laws, a clunky name for legislation that reduces income to unions.

Unions are fighting back, trying to build a retaining wall in Virginia and elsewhere against an anti-labor tide that began in 2012 with key victories for conservatives and business groups in the Midwest. Since then, four states have passed right-to-work statutes. That brought the number of states with such laws to 26.

[Right-to-work measure headed for Virginia ballot.]

Virginia has been right-to-work by statute since 1947, but Question 1 on state ballots on Nov. 8 would enshrine the policy in the state constitution. Repeal would then be far more difficult for future governors and state legislators.

“We don’t really have a lot of control over what future General Assemblies will do,” said Nicole Riley, Virginia director of the National Federation of Independent Business. “It’s a way of making sure that the robust business environment here in Virginia would be secured.”

Right-to-work laws protect employees against being required to join a union, which means unions end up representing people who don’t pay dues.

Business groups say right-to-work laws guarantee individual freedom and encourage investment to create jobs. Unions say they suppress wages and increase income inequality.

The surge of interest in right-to-work is evident in the number of states where it’s an issue in this year’s balloting.

In Alabama, voters will vote on a constitutional amendment similar to Virginia’s. Ten other states already have right-to-work language in their constitutions, according to the AFL-CIO.

In Missouri, a Republican victory in the governor’s race would almost certainly mean that state would switch to right-to-work. Right-to-work also could advance with Republican victories in the Montana governor’s race and in some legislative races in Kentucky, according to right-to-work supporters.

[How the birthplace of the American labor movement just turned on its unions.]

Some of the contests are drawing national attention, as out-of-state business and labor interests pour in money.

Spending on television ads in the Missouri gubernatorial battle has reached $27.5 million, making it the nation’s most expensive governor’s race. Former Navy officer David Greitens (R) and Attorney General Chris Koster (D) are vying to succeed Gov. Jay Nixon (D), who vetoed right-to-work legislation this year.

In Virginia, both sides said they expect a close vote, with large numbers of voters still undecided or unfamiliar with the issue. One concern is that the text of the ballot question is lengthy and complicated, so many voters may find it confusing.

The General Assembly passed a resolution along party lines in February putting the issue on the ballot, with Republicans in favor and Democrats opposed.

Gov. Terry McAuliffe (D) opposes the measure, but governors can’t veto resolutions to amend the state constitution.

Unions are relying on mobilizing their membership to block the amendment. About 100 spirited activists gathered early on a recent Saturday in a union office in Annadale before fanning out with addresses of union households to visit and literature to distribute.

“What time is it? Union time!” the group chanted.

Leaders said their members were energized by what they see as a national attempt to break unions. They also saw the bid to put right-to-work in the Virginia constitution as an unnecessary political stunt, given that nobody has been trying to overturn the law.

“It’s just trying to step on people when they’re down,” said Daniel W. Duncan, president of the Northern Virginia Labor Federation. “It’s made our members mad. It’s got them worked up.”

He noted that 5.4 percent of Virginia workers were members of unions in 2015, well below the national average of 11.1 percent, according to the U.S. Labor Department.

Business groups and others supporting the amendment are encouraging companies to spread the word about it to employees and their families. They plan to run some television advertising in the Hampton Roads area and possibly in Richmond and to do some print and digital advertising. But they fear unions are doing more.

[Laws that may decimate unions may be inevitable.]

That worries Del. Richard P. Bell (R-Staunton), the principal sponsor of the amendment, who has worked since 2010 to put it on the ballot.

“Our efforts, compared to efforts by unions, who are investing heavily in it, are pretty weak,” Bell said. Supporters have “not engaged in any kind of get-out-the-vote campaign to this point,” he said.

The unions say they’re relying on door-to-door canvassing because they can’t afford television advertising. “I would not call this a large dollar-amount campaign,” Gina Maglionico, communications director for the Virginia AFL-CIO, said.

The Virginia amendment reached the ballot partly in response to a national wave of anti-union sentiment, according to Bell and other supporters.

Business groups saw a need for Virginia to strengthen its commitment to right-to-work to protect its competitive advantage as other states embraced the policy.

“For the longest period of time, Virginia was the northernmost right-to-work state, and we used that to good advantage,” Paul Logan, communications director for the Virginia Chamber of Commerce, said. “Now you’ve got the likes of Michigan, well to the north of us, as right-to-work.”

The key breakthrough for right-to-work came in 2012, when Michigan and Indiana adopted laws. Wisconsin adopted right-to-work in 2015, and West Virginia did so this year.

The movement gained strength when GOP legislators around the country saw that Michigan Republicans who voted in favor of right-to-work didn’t lose their seats as a result, according to Greg Mourad, vice president of the National Right to Work Committee.

“Wisconsin happened just a few months after the election that proved it was safe in Michigan,” he said.

States have embraced right-to-work also in hope of attracting corporate investment after losing large numbers of manufacturing jobs since the 2008 recession.

“We’ve seen a number of reports from site selection consultants,” Mourad said. “When their clients want to move manufacturing facilities, they don’t even consider states without right-to-work.”

Unions and their supporters counter that other factors — such as a well-educated workforce and good roads and transit — are more important than right-to-work laws in attracting investment.

They also point to data showing that wages are lower in right-to-work states, leading to the union joke that a better description of the policy would be “right-to-work for less.”

Wages are 3 percent lower in right-to-work states than other states, after accounting for differences in the cost of living, demographics and labor-market characteristics, according to an April 2015 study by the Economic Policy Institute. That translates to $1,558 a year less in earnings for a typical full-time worker.

Gebre cites that argument in his pitches to voters in Virginia. He and other canvassers targeted union households because they were likely to be most receptive and because the unions didn’t have enough resources to contact all voters.

“Around the country, they want us unions to get out of the way so they can fire anybody, so they can further depress wages,” Gebre says.

He had success with an electricians union member in Woodbridge.

“I’ll vote no,” said the middle-aged man, who asked not to be identified by name.

As Gebre walked away, he said the voter, like many, hadn’t been aware of the measure. Gebre added, “He said he was waiting for the union to tell him which way to vote.”