INDIANAPOLIS -- Nearly a year after legislatures in Wisconsin and several other Republican-dominated states curbed the power of public-sector unions, lawmakers are turning their sights toward private-sector unions, setting up what is sure to be another political storm.

The thunderclouds are gathering first here in Indiana. Leaders of the GOP-controlled Legislature say that when the legislative session opens Wednesday, their No. 1 priority will be to push through a business-friendly measure known as a right-to-work law.

If Indiana enacts such a law -- and its sponsors say they have the votes -- it will give new momentum to those who have previously pushed such legislation in Maine, Michigan, Missouri and other states. New Hampshire's Republican-controlled Legislature was the last to pass a right-to-work bill in 2011, but it narrowly failed to muster the two-thirds majority needed to override a veto by the Democratic governor; an Indiana law would re-energize that effort.

Right-to-work laws prohibit union contracts at private-sector workplaces from requiring employees to pay any dues or other fees to the union. In states without such laws, workers at unionized workplaces generally have to pay such dues or fees. Many right-to-work supporters say it is morally wrong to force unwilling workers to contribute to unions, while opponents argue that it is wrong to allow "free riders" not to support unions that represent them in negotiations and arbitrations.

Right-to-work is also a potent political symbol that carries serious financial consequences for unions. Corporations view such laws as an important sign that a state has policies friendly to business. Labor leaders say allowing workers to opt out of paying any money to the union that represents them weakens unions' finances, bargaining clout and political power.

Organized labor has vowed to fight the Indiana bill. If the legislation passes, Indiana would become the first state to have such a law within the traditional manufacturing belt, a union stronghold that stretches from the Midwest to New England. Right-to-work laws exist in 22 states, almost all in the South and West, with Oklahoma the most recent to pass one, in 2001.

Right-to-work supporters say they can win quick passage because Indiana's Republican governor, Mitch Daniels, backs the bill and Republicans have large House and Senate majorities.

Democratic and union leaders say they hope to block the legislation, in part by flooding the statehouse with thousands of protesters -- exactly as unions did last year in Wisconsin, Ohio and Indiana in an attempt to defeat legislation that limited bargaining rights for public-sector workers. Indiana's Democratic lawmakers also have hinted that they might once again flee to Illinois, as they did last year, to block votes on anti-union bills.

Indiana's GOP leaders are eager to pass the bill -- and end any related commotion -- before Feb. 5, when the national spotlight turns to Indianapolis for the Super Bowl.

In Indiana, 8.2 percent -- or 178,779 -- of the state's private-sector workers belong to unions, compared with 6.9 percent nationwide. That is down from more than 20 percent three decades ago.