"We've had no increase in construction jobs - they've remained flat - we've had a decline of 5,000 in mining and a decline of 2,200 in manufacturing," Roberts said. "That may well help explain why there are fewer union members working."
The federal figures show the number of union members who are working. They do not show unions' total membership, so some union workers in struggling sectors, like construction, could remain in a union but without a union job.
Some laid-off union members also expect to return to work. About 5,000 mining and logging jobs were lost last year, according to state workforce figures. Not many of those were union members, said United Mine Workers of America spokesman Phil Smith, but those that were may return to work and boost the ranks of working union members.
Smith said about 300 laid-off miners in Boone County are expecting to return to work at some point, for instance.
"Those will be union jobs that will jump up," Smith said.
Nationally, union membership is shrinking.
The number of union workers stood at 14.4 million in 2012, down from 17.7 million union workers in 1983.
Perdue said unions are under siege from the wealthy and from outsourcing.
"I think there is an out-and-out attack by the wealthy to eliminate a class of workers, and that is union membership," Perdue said.
Roberts said it was ironic that union membership was down with a union-friendly Democrat in the White House.
"They've got more voice and less jobs," Roberts said.