Morgan also says the union label still is appealing in working-class communities where organized labor already has a foothold.

"If you're a low-wage worker living on the north side of Philadelphia or the West Side of Chicago, the only person who owns a house or has a lawn mower ... the only person making a decent living is someone with a union job," he says.

Though some unions have been forced to make concessions to save jobs in recent years, wages still can be very attractive.

Michael Bronson, who's starting an apprenticeship next month at Ironworkers Local 55 in northwest Ohio, expects to someday nearly triple the salary he's earned as an auto mechanic.

"For 10 years, I thought it was as good as it was going to get," says the 28-year-old Bronson. "I was just settling for whatever was offered. I was making $11 an hour and I had no health benefits. That was my future. ... You're expendable. They can pick up another guy at $8.50 and fire you."

Bronson began looking for a union job after noticing his in-laws â¿¿ including a pipefitter â¿¿ didn't share his financial pressures. "I knew they didn't live like I did, paycheck to paycheck, wondering what's going to happen next month," he says. "That's what persuaded me."

When he completes a four-year apprenticeship, Bronson expects an hourly wage of about $30. "Middle class to me is heaven," he says. "I've been $10,000 below poverty the last 10 years."

Six months ago, Bronson knew nothing about unions. Now he's a convert.

"It's kind of like a religion," he says. "Once you realize what a good union can do for you, you'll live it the rest of your life and you'll push it on everybody."

That attitude isn't universally shared. Approval of unions hovered around 60 percent through 2008, but it's now 52 percent, according to a 2012 Gallup poll. There's great political disparity: The favorability rate among Democrats is 74 percent; among Republicans, it's 31 percent.

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