In a year when teachers and autoworkers mounted lengthy strikes, participation in labor unions in 2019 continued their decades-long decline.

Union membership in the American workforce was down to 10.3 percent from 10.5 percent in 2018, according to statistics released Wednesday by the Bureau of Labor Statistics.

The continued slide shows how energy and momentum around the labor movement is not translating into equivalent growth for unions, whose memberships have fallen sharply as a percentage of the U.S. workforce over the past roughly 40 years. In 1983, unions represented about 1 out of 5 workers; now it’s 1 in 10 workers.

“They’re disappointing numbers for workers and unions,” said Professor Joseph McCartin, the executive director of the Kalmanovitz Initiative for Labor and the Working Poor at Georgetown University. “The expansion of the labor market in 2019 didn’t produce a proportional expansion in union members. Unions would have hoped to make gains in the course of the past year and they didn’t.”

The number of total union members — 14.6 million — is relatively unchanged from 2018. But in a robust jobs market, the number of union workers added has not been enough to replace those who retired or left the workforce.

The drop in union representation in the workforce is sobering news for the labor movement, which otherwise saw an eventful year.

Major strikes including grocery workers in the Northeast, teachers in cities such as Chicago and Little Rock, Ark., and autoworkers around the country attracted public attention and became a crucial stop for 2020 candidates on the campaign trail. The 47,000 General Motors workers who brought the company’s car production to a halt during a six-week strike that culminated with a contract — and concessions — from the company in the fall marked one of the largest private-sector strikes in the last 20 years.

And even nonunion workers have taken advantage of the tight labor market to advocate for more workers’ rights. Employees have circulated petitions around Silicon Valley companies, calling for tech companies to cut ties with immigration enforcement, and gig-economy drivers at Lyft and Uber have rallied for better pay and more rights.

The numbers of workers who participated in large-scale strikes ballooned to 500,000 in 2018, up from 25,000 in 2017, according to the Bureau of Labor Statistics. Strike participation numbers for 2019 have yet to be finalized.

But the broader factors that have contributed to union declines over the last few decades appear to still be in play.

“The lack of an increase in union membership points to the fact that there are still so many barriers to organizing,” said Heidi Shierholz, the director of policy at the Economic Policy Institute. “When people try to organize at their workplace there is just a relentless, fierce opposition on the part of employers.”

One reason why union membership may have declined is that 2019 was the first full year since the Supreme Court’s decision in the Janus case. The court ruled that it was unconstitutional to allow unions to require collective bargaining fees from public employees — a decision that was seen as a major blow for unions and their budgets.

Local public employees saw a small dip in membership to 39.4 percent in 2019, down from 40.3 the previous year, Shierholz noted. But union membership among state government workers has grown.

Public support for unions appears to be growing. Some 64 percent of people said they approved of unions last year, among the highest numbers the company has collected in the last 50 years, according to Gallup. And nearly half of nonunion workers say they would join a union if given the opportunity to do so — a 40-year high.

“People look at decline of unionization and think that people don’t want unions anymore,” Shierholz said. “But its just demonstrably false.”

The momentum in the labor movement has fostered a political discussion on the left about workers’ rights and strengthening the labor movement.

Sen. Bernie Sanders (I-Vt.) wants to give federal workers the right to strike and ban “at will” employment, which allows companies to fire workers without cause. Sen. Elizabeth Warren (D-Mass.) has called for banning the permanent replacement of striking workers and strengthening the National Labor Relations Board, which enforces laws meant to protect unions and organizing in workplaces.

Both of them, along with Democratic presidential candidate Pete Buttigieg, say they want to undo “right to work” laws that Republicans have championed in states throughout the country that allow workers to opt out of paying union dues.

Some labor advocates said that union participation could eventually rise if worker strikes fortify the political will to make changes like these.

“The way that huge upsurges in union membership have happened in this country is when workers have taken control, gone on massive strikes and forced corporate elite to enter grand bargains,” said Jane McAlevey, a former labor organizer and the author of “A Collective Bargain: Unions, Organizing and the Fight for Democracy."

McAlevey noted that previous waves of unionization — in the 1930s after the National Labor Relations Act passed, and a few decades later as the public sector began to unionize — were preceded by large scale strikes.

“Strikes are a precursor,” she said. "I believe we’re at the beginning of that cycle.”

The International Association of Fire Fighters is one of the larger unions that has seen growth over the years. The union was at 321,000 last year up, from 220,000 20 years ago. Harold Schaitberger, the union’s general president, said their success is due to showing their members the benefits the union helped secure for them, including better government codes on firefighting and success in collective bargaining.

“There’s a direct connection to what the union does to having tangible effect on their lives,” he said.

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