"Unions have lost power in the private sector over time because of competition, globalization, and the fact that they don't add any value to worker productivity," said Chris Edwards, an economist with the Cato Institute and a fan of right-to-work laws.

Businesses are responding to today's realities and "can't pay above-market wages forever," he said. "So either they will move work abroad or they will automate to try to get rid of as many workers as they can."

To build jobs in America, Edwards said businesses can't be beholden to mandatory collective bargaining, which can increase wages and expenses without increasing profits.

In recent years, the retirement of baby boomers has fueled anti-union sentiment as some companies struggle to pay pensions as well as health care for the aging population -- benefits that were negotiated through collective bargaining. And, Edwards notes, that pressure comes on top of the economic downturn.

"Unions are going the way of the dinosaur in the U.S. private sector, which is a good thing for workers and businesses because it will make America more competitive," he said. "If right-to-work laws extend to the 50 states, then private sector unions will be dead in America."

How does Edwards feel about the death of all private sector unions?

"Good riddance," he said.

Is it all about red vs. blue?

The decline in union strength is also tied to the political battle between Democrats and Republicans.

"There has been a recognition by both the unions and people who are not happy with unions in the last 12 years or so that unions have been fundamentally the powerhouse between the Democratic party and their electoral math," said Linda Kaboolian, lecturer on public policy with Harvard's Kennedy School of Government.

Unions provide money and put "boots on the ground" to get Democratic candidates elected. If they shrink, so will the money and power of that central blue voting bloc, Kaboolian said, adding that "it's a perfectly rational point of view" for right-wing organizations to take.

Union organizers did a great deal to push for President Barack Obama's re-election in key states, including Michigan. The president himself paid a visit to the state this week, voicing his opposition to the state's right-to-work measure.

"What we shouldn't do is take away your rights to bargain for better wages," Obama told workers. "These so called right to work laws don't have to do with economics, they have to do with politics."

Kaboolian insisted that economic arguments for slicing union strength don't add up. Even if unionized workers cost more, they can often prove to be a higher-quality work force that will last, grow and learn new skills, she says.

Kaboolian speaks of her own experience, having served as a union officer at the University of Michigan. She was also a manager and a worker in both unionized and non-unionized agencies. She said she does not advocate for or against right-to-work laws.

James Sherk of the conservative Heritage Foundation rejected the idea that unions' decline are tied to American politics.

He said the changes are being driven "by efforts to attract business," not an underhanded political effort, he says.

"We're coming out of a pretty nasty recession ... Businesses understandably don't want to be unionized."