Wisconsin’s Republican state legislature pressed ahead with their plan to enact “right to work” legislation aimed at curbing union power, clashing with labor leaders at a contentious committee meeting on Tuesday.

Hundreds of union members roared in protest against the bill outside the state capitol in Madison. The demonstration was reminiscent of, if far smaller than, the huge protests in 2011 that sought to stop Governor Scott Walker, a possible 2016 presidential candidate, from enacting a law curbing collective bargaining for most of the state’s public sector unions.

Republicans on Tuesday hailed the right-to-work legislation, saying it would promote employee freedom and economic competitiveness. But opponents of the bill – which would make Wisconsin the nation’s 25th right-to-work state – insisted that its underlying purpose was to weaken labor unions and that its result would be lower wages.

Legislative leaders have called an extraordinary session to take up the bill, which would bar any requirement that employees at private sector workplaces pay union fees. Republicans are in firm control of both houses of the Wisconsin legislature and Walker has said he would sign the bill if it is sent to him.

Scott Fitzgerald, the Wisconsin senate majority leader and author of the bill, testified at Tuesday’s hearing, saying the legislation would be a “game changer” for Wisconsin in attracting business. Wisconsin Republicans say their state needs to enact right-to-work legislation to remain competitive because nearby Indiana and Michigan have adopted such laws in recent years.

Fitzgerald said: “This issue, at its heart, is about worker freedom.” The legislation, he said, would bar any requirement that private sector workers join unions – even though under federal law private sector workers already cannot be required to join unions.

Kevin Flynn, left, and Knut Lombard, both members of the International Union of Operating Engineers, join labor workers in a rally outside the Wisconsin state capitol on Tuesday. Photograph: John Hart/AP

The session began as the executive committee of the AFL-CIO, the main federation of US unions, was holding its winter meeting in Atlanta. Labor leaders denounced the developments at the meeting, with several union presidents complaining that right-to-work bills encourage “free riders” who can opt out of paying union fees, depleting union treasuries, while continuing to receive union representation and services such as grievance hearings.

“This right to work sham is about much more than unions,” Richard Trumka, the AFL-CIO’s president, said in a statement. “It is simply the next step in the billionaire rightwing’s attempt to strip our freedoms to bargain with our employers as we see fit, ensure safe workplaces and raise wages across the country.”

Republicans are pressing ahead, even though Walker just a few months ago cautioned the legislature not to take up right to work. In December he said: “As I said before the election and have said repeatedly over the last few years, I just think right-to-work legislation right now ... would be a distraction from the work that we’re trying to do.”

Last fall, Walker moved to the middle politically as he sought to attract moderates while running for re-election. In recent weeks, as he considers a presidential run, he has pivoted right to woo conservatives – on abortion, right to work and other issues.

Fitzgerald said he called the extraordinary session on short notice to avoid a replay of the giant 2011 protests. “It sends a strange message to people outside of Wisconsin that maybe Wisconsin isn’t the place to expand your business or to certainly locate,” he told the Associated Press.

Phil Neuenfeldt, president of the Wisconsin AFL-CIO, denounced the extraordinary session. “If right to work was any good for this state, we wouldn’t see it being tried to pass this quickly, with limited debate in an attempt to circumvent democracy,” he said.

John Ahlquist, a University of Wisconsin political scientist, said he thought the session was timed to take the public’s focus off the much-criticized budget cuts Walker had proposed, especially to the university.

Ahlquest said the legislation was about far more than competitiveness. “More than anything else, right to work is to make it harder for unions,” he said. “The primary goal is to weaken them, to weaken the base of the Republicans’ political opponents.”

Scott Marley, the top lobbyist for Wisconsin Manufacturers and Commerce, has pushed hard for right to work, saying it helped Indiana attract thousands of jobs. “If we don’t pass right to work, we really risk falling behind in Wisconsin and putting ourselves at a competitive disadvantage for job-creation projects,” he said in a video.

Testifying against the legislation on Tuesday, Gordon Lafer, a University of Oregon professor of labor studies, pointed to a study saying wages in right-to-work states are 3.2% below those in non-right-to-work states. “If right to work didn’t lower wages and benefits, there would be no reason to think it would draw new employers into the state,” he said.

