Some 7,500 labor supporters waved signs and shouted "Veto!" as they marched into the Indiana Statehouse to protest a right-to-work bill, the first approved in an industrial state.

The year was 1957, and a Republican-controlled legislature had just approved the bill and sent it to Gov. Harold W. Handley, who said he didn't like the legislation but would allow it to become law without his signature. When the protesters learned he wouldn't deliver the veto, they pushed past police officers guarding Handley's office.

The governor slipped away through a side exit. The state's right-to-work law went into effect, only to be repealed nine years later.

Is history about to repeat itself? SB 395 would make it illegal to require an employee to join or remain a member of a union, and pressure from anti-union forces on seemingly reluctant GOP leaders is growing. And just as they did in 1957, organized labor is pushing back. Here's a primer on what the conflict entails:

Q. What would the right-to-work law do?

A. It would prohibit union membership and dues as a condition of employment.

Q. Why is it controversial?

A. Supporters say that union requirements discourage employers from locating in Indiana; opponents charge that right-to-work legislation drives down worker wages – a "right-to-work-for-less bill," they insist.

Q. Who is right?

A. It depends on whose research you choose. Richard Vedder, an Ohio University economist, is the go-to guy for right-to-work proponents. In a report he did for the Indiana Chamber of Commerce, he argues that states with right-to-work laws have "generally been more prosperous and have had higher rates of economic growth. Moreover, people have moved in large numbers to right-to-work states, signaling that many perceived that these states offer a higher quality of life."

Vedder and his associates claim that if Indiana had adopted a right-to-work law in 1977, annual per-capita income by 2008 would have been $2,925 higher.

"Nearly $19 billion in annual income was lost because of Indiana's lack of right-work-law," according to the study. "Indiana grew far slower than the nation as a whole in the last three decades, and most (about two-thirds) of this 'growth deficit' is explainable by Indiana's lack of a right to work environment."

Vedder's assertion seems to be that freedom from union requirements is the quality-of-life attraction in those states. But it's hard to look at a map and ignore the climate connection, and numerous academic observers have attributed the availability of air conditioning as a major factor in U.S. migration. Did jobs flow to the South and West because of right-to-work laws or because they followed booming population growth and consumer and housing demand?

Right-to-work opponents cite research from academics such as Lonnie Stevans of Long Island's Hofstra University: "While the number of self-employed is higher and business bankruptcies lower on average in right-to-work states, there is no significant difference in capital formation or employment rates, (all other things being equal)," he wrote in a 2009 report on right-to-work laws. "In addition, per-capita personal income and wages are both lower, yet proprietors' income is higher in right-to-work states."

From U.S. Bureau of Labor Statistics reports, two points are abundantly clear:

•The states with the five lowest union membership rates all are right-to-work states: North Carolina, Arkansas, Georgia, Louisiana and Mississippi.

None of the five states with the highest union membership have right-to-work laws: New York, Alaska, Hawaii, Washington and California.

•Union members earn more than non-union members: "In 2010, among full-time wage and salary workers, union members had median usual weekly earnings of $917, while those not represented by unions had median weekly earnings of $717," according to a January BLS report.

Q. Isn't approval assured with a Republican majority in both chambers of the legislature?

A. Not necessarily. Indiana House Democrats drew a line in the sand in the opening moments of the new session, calling for bills on first reading to be read individually.

They wanted to take advantage of a rule allowing them to object to introduction of the right-to-work legislation, including HB 1028 and HB 1468, the latter of which is scheduled for a vote in the House Employment, Labor and Pensions Committee at 9 a.m. Monday.

Veteran lawmakers surely haven't overlooked the labor opposition.

About 600 steelworkers rallied at the Statehouse last Tuesday to protest the "anti-worker agenda,"including the right-to-work bills.

Rep. Douglas Gutwein, chairman of the labor committee, told The Associated Press last week that he believes a right-to-work law would help Indiana's economy but said issues such as the state budget and changes to the education system might take precedence over action on the bill.

The National Right to Work Committee, actively pushing the Indiana legislation, targeted House Speaker Brian Bosma in a recent mailing, accusing the Indianapolis Republican of "pulling strings behind the scenes" to stop the legislation because he hopes to run for statewide office.

Q. Does Gov. Mitch Daniels support the bill?

A. Yes, he said he would sign if approved. But he also said it wasn't on his agenda, clearly recognizing how divisive it would be.

Riling a segment of the electorate hostile to right-to-work legislation could derail his other legislative aims – such as weakening teachers' collective bargaining rights – that might otherwise go unnoticed by labor supporters.

Q. There was no discussion of right-to-work laws in the last election – why is it coming up now?

A. Credit the powerful National Right to Work Committee.

Its single aim is to fight compulsory union membership.

While it doesn't disclose its source of funding, it operates an aggressive direct-mail fundraising campaign and is believed to have extensive support from conservative foundations.

The organization has used November's GOP landslide to full advantage.

In addition to Indiana, right-to-work legislation is being pushed in Missouri, New Hampshire, Maine, Minnesota and even Michigan, where lawmakers have introduced legislation that would allow local governments to create "right-to-work zones."

The strongest pushback is found in Wisconsin, where more than 10,000 residents descended on the statehouse to protest Republican Gov. Scott Walker's bid to strip all public employees, including teachers, of collective bargaining.

Q. What should we expect as the outcome in Indiana?

A. It's tough to say, given the General Assembly's last makeover. Veteran lawmakers might fear the backlash from organized labor in 2012.

But the Senate has 12 members who have never faced re-election and almost 20 percent of House members have never done so, and the rookies on both sides are decidedly more conservative than their predecessors. They've demonstrated so far a willingness to advance measures that others declined to touch, and they might just push more-cautious GOP leaders to repeat the 1957 session.