The typical union worker now is more likely to be an educator, office worker or food or service industry employee rather than a construction worker, autoworker, electrician or mechanic. Far more women than men are among the union-label ranks.
In a blow to public sector unions, the Supreme Court ruled this week that thousands of health care workers in Illinois who are paid by the state cannot be required to pay fees that help cover a union's cost of collective bargaining.
The justices said the practice violates the First Amendment rights of nonmembers who disagree with stances taken by unions.
The ruling was narrowly drawn, but it could reverberate through the universe of unions that represent government workers. The case involved home-care workers for disabled people who are paid with Medicaid funds administered by the state.
Also in June, a California judge declared unconstitutional the state's teacher tenure, dismissal and layoff laws. The judge ordered a stay of the decision, pending an appeal by the state and teachers union.
"The basic structure of the labor union movement has changed, reflecting changes in the economy," said Ross Baker, a political science professor at Rutgers University. "Manufacturing is a diminishing segment of the economy. Also, a lot of the manufacturing that's being done today is being done nonunion."
Union members continue to be a powerful political force in politics, and Baker said he didn't see the role of unions diminishing. "I just think the colors of the collars are changing," Baker said.
In 2013, 14.5 million workers belonged to a union, about the same as the year before. In 1983, the first year for which comparable figures are available, there were 17.7 million union workers.
The largest union is the National Education Association, with 3.2 million members. It represents public school teachers, administrators and students preparing to become teachers.
Next is the 2.1-million Service Employees International Union. About half its members work in the public sector.
The American Federation of State County and Municipal Employees has 1.6 million, followed by the American Federation of Teachers with 1.5 million and the International Brotherhood of Teamsters with 1.4 million.
There are 1.3 million members in the United Food and Commercial Workers International Union.
Until four years ago, the unionization rate was far higher in the private sector than in the public sector. Now the roles are reversed.
But it's been a bumpy road for public unions in some Republican-governed states.
In 2011, Gov. Scott Walker, R-Wis., took on public sector unions forcefully soon after he was swept into office. He got enacted a bill effectively ending collective bargaining for most public workers in the state. He withstood huge labor demonstrations at the state Capitol and then became the first governor in U.S. history to defeat a recall attempt. The law has been challenged in court, and continues to be. But its main thrust so far has been upheld.
A sign of the decline of traditional labor unions came in May when the United Automobile Workers raised its membership dues for the first time in 27 years to help offset declining membership. Also, the defeat in February of the UAW's effort to unionize workers at Volkswagen's Chattanooga, Tennessee, plant was a setback to labor.
A 2013 Gallup poll showed that 54 percent of Americans said they approved of labor unions, down from the all-time high of 75 percent in both 1953 and 1957.
"Labor unions play a diminishing role in the private sector, but they still claim a large share of the public sector workforce," says Chris Edwards, director of tax studies at the libertarian, free-market Cato Institute.
"Public sector unions are important to examine because they have a major influence on government policies through their vigorous lobbying efforts. ... They are particularly influential in states that allow monopoly unionization through collective bargaining."
Since 2000, factories have shed more than 5 million jobs. Five states Virginia, North Carolina, South Carolina Georgia and Texas ban collective bargaining in the public sector.
Follow Tom Raum on Twitter: http://www.twitter.com/tomraum