MADISON, Wis. — Rallies were held across the U.S. to support thousands of protesters holding steady at the Wisconsin Capitol in their fight against Republican-backed legislation aimed at weakening unions.

Union supporters organized rallies Saturday from New York to Los Angeles in a show of solidarity as the protest in Madison entered its 12th straight day and attracted its largest crowd yet: more than 70,000 people. Hundreds banged on drums and screamed into bullhorns inside, while others braved frigid weather and snowfall during a rally that spilled into city streets.

"I want to thank you for coming out here today to exercise those pesky First Amendment rights," actor Bradley Whitford, who starred in television's political drama "The West Wing," told his hometown crowd. "This governor has to understand Wisconsin is a stubborn constituency. We fish through ice!"

Republican Gov. Scott Walker has introduced a bill that includes stripping almost all public workers, from librarians to snow plow drivers, of their right to collectively bargain on benefits and work conditions. Walker has said the bill would help close a projected $3.6 billion deficit in the 2011-13 budget. He also argues that freeing local governments from collective bargaining would give them flexibility amid deep budget cuts.

The bill has sent Democrats and unions into an outrage nationwide. They see it as trampling on workers' rights and as an attempt to destroy Democrats' strongest campaign allies.

"Wisconsin is opening up people's eyes a little bit," said Jay Van Loenen, a teacher who attended a rally in Denver that attracted about 1,000 people. "So I think that the move is to try to get people more involved in their unions and create a stronger front so that if something happens here, we are prepared."

Several thousand people gathered for a rally in Columbus, Ohio, where lawmakers are considering a similar bill. Indiana Democrats successfully blocked a Republican bill last week that would have prohibited union membership from being a condition of employment.

Large crowds of teachers, firefighters and public workers also gathered for rallies -- holding American flags, wearing pro-union clothing and holding signs -- in other capital cities including Topeka, Kansas; Harrisburg, Pennsylvania; and Olympia, Washington state.

In Los Angeles, public sector workers and others held signs that read "We are all Wisconsin." Some wore foam "cheeseheads," the familiar cheese-slab hats worn by Green Bay Packers fans. Wisconsin is known for its dairy farms.

Covered in layers of coats, scarves, hats and gloves, about 1,000 rallygoers outside the Minnesota Capitol in St. Paul chanted "Workers' rights are human rights" and waved signs, some reading "United we bargain, divided we beg."

"The right to collectively bargain is an American right," Eliot Seide, a local union leader, told the crowd in St. Paul. "You can't have American democracy if you don't have a strong trade union movement."

The rallies were part of a campaign by the liberal online group MoveOn.org to hold demonstrations supporting Wisconsin workers in major cities across the country. Some of the demonstrations attracted counter-protests by supporters of the conservative tea party movement, though the pro-union rallies were larger.

Madison Police spokesman Joel DeSpain said he didn't have a firm estimate on the Wisconsin capital's crowd, but said it was larger than last weekend when nearly 70,000 people descended on the Capitol.

The crowd cheered as pilot Jeff Skiles, the first officer on the US Airways Flight that landed in New York City's Hudson River in January 2009, told them that "justice and righteousness will always win out." Skiles helped pilot Chesley "Sully" Sullenberger land the plane, whose 155 passengers and crew members were safely rescued.

Protesters jammed the Wisconsin Capitol steps, packed the ice-covered lawn -- some sat in trees -- and filled surrounding streets. Several thousand counter-protesters came out last Saturday to support Walker, but they were hardly visible this time.

Some protesters have even been sleeping in the Wisconsin Capitol. Police planned to let protesters stay overnight Saturday into Sunday but are expected to finally close the building Sunday afternoon for cleaning.