MADISON, Wis. - A group of Democratic Wisconsin lawmakers blocked passage of a sweeping anti-union bill Thursday, refusing to show up for a vote and then abruptly leaving the state in an effort to force Republicans to the negotiating table.

As ever-growing throngs of protesters filled the Capitol for a third day, the 14 Democrats disappeared around noon, just as the Senate was about to begin debating the measure, which would end a half-century of collective bargaining rights for most public employees.

Hours later, one member of the group told The Associated Press that they had left Wisconsin.

"The plan is to try and slow this down because it's an extreme piece of legislation that's tearing this state apart," Sen. Jon Erpenbach said in a telephone interview.

Democrats hoped Republican Gov. Scott Walker and GOP lawmakers would consider revisions to the bill.

Walker, who took office just last month, urged the group to return and called the boycott a "stunt."

"It's more about theatrics than anything else," he said. The governor predicted the group would come back in a day or two, after realizing "they're elected to do a job."

Walker said Democrats could still offer amendments to change the bill, but he vowed not to concede on his plan to end most collective bargaining rights.

With 19 seats, Republicans hold a majority in the 33-member Senate, but they are one vote short of the number needed to conduct business. So the GOP needs at least one Democrat to be present before any voting can take place. Once the measure is brought to the floor, it needs 17 votes to pass.

Other lawmakers who fled sent messages over Twitter and issued written statements but did not disclose their location.

Erpenbach said the group had been in Rockford, Ill., but they dispersed by late afternoon and were all still outside Wisconsin.

In response to a question of where she was, Sen. Lena Taylor sent a tweet saying she was "doing the people's business. Power to the PEOPLE."

As Republicans tried to begin Senate business Thursday, observers in the gallery screamed "Freedom! Democracy! Unions!" Opponents cheered when a legislative leader announced there were not enough senators present to proceed.

The sergeant-at-arms immediately began looking for the missing lawmakers. If he cannot find them, he's authorized to seek help, including potentially contacting police.

Senate rules and the state constitution say absent members can be compelled to appear, but it does not say how.

"Today they checked out, and I'm not sure where they're at," Republican Senate Majority Leader Scott Fitzgerald said. "This is the ultimate shutdown, what we're seeing today."

Elsewhere, some Democrats applauded the developments in Wisconsin as a long-awaited sign that their party was fighting back against the Republican wave created by November's midterm election.

"I am glad to see some Democrats, for a change, with a backbone. I'm really proud to hear that they did that," said Democratic state Sen. Judy Eason-McIntyre of Oklahoma, another state where Republicans won the governorship in November and also control both legislative chambers.

Across the Wisconsin Statehouse, Democrats showed up in the Assembly chamber wearing orange T-shirts that proclaimed their support for working families.

After a routine roll call, they exchanged high-fives with protesters, who cried "thank you" as the Democrats walked by. Protesters unleashed venomous boos and screams at Republicans.

Thursday's events were reminiscent of a 2003 dispute in Texas, where Democrats twice fled the state to prevent adoption of a redistricting bill designed to give Republicans more seats in Congress. The bill passed a few months later.

The drama in Wisconsin unfolded in a jam-packed Capitol. Madison police and the State Department of Administration estimated the crowd at 25,000 protesters, the largest number yet.

Demonstrators stood shoulder-to-shoulder in the building's hallways, sat cross-legged across the floor and made it difficult to move from room to room.

Protesters clogged the hallway outside the Senate chamber, beating on drums, holding signs deriding Walker and pleading for lawmakers to kill the bill. Some others even demonstrated outside lawmakers' homes.

Hundreds of teachers joined the protest by calling in sick, forcing a number of school districts to cancel classes. Madison schools, the state's second-largest district, with 24,000 students, closed for a second day.

Thousands more people, many of them students from the nearby University of Wisconsin, slept in the rotunda for a second night.

"We are all willing to come to the table. We've all been willing from day one," said Madison teacher Rita Miller. "But you can't take A, B, C, D and everything we've worked for in one fell swoop."

About 12 law enforcement agencies were helping guard the Capitol, which was scheduled to remain open around the clock for an indefinite period.

Dane County Sheriff Dave Mahoney said authorities were ordered to show "extreme measures of tolerance."

"What we're seeing here is perhaps the most dramatic exercise of the democratic process," Mahoney said. "We're not only protecting the rights of organized labor, but also the rights of people supporting the bill."

Nine people were given citations for minor acts of civil disobedience, he said.

The proposal marks a dramatic shift for Wisconsin, which passed a comprehensive collective bargaining law in 1959 and was the birthplace of the national union representing all non-federal public employees.

In addition to eliminating collective-bargaining rights, the legislation also would make public workers pay half the costs of their pensions and at least 12.6 percent of their health care coverage - increases Walker calls "modest" compared with those in the private sector.

Republican leaders said they expected Wisconsin residents would be pleased with the savings the bill would achieve - $30 million by July 1 and $300 million over the next two years to address a $3.6 billion budget shortfall.

"I think the taxpayers will support this idea," Fitzgerald said.

Wisconsin has long been a bastion for workers' rights. But when voters elected Walker, an outspoken conservative, along with GOP majorities in both legislative chambers, it set the stage for a dramatic reversal of the state's labor history.

Under Walker's plan, state employees' share of pension and health care costs would go up by an average of 8 percent.

Unions still could represent workers, but could not seek pay increases above those pegged to the Consumer Price Index unless approved by a public referendum. Unions also could not force employees to pay dues and would have to hold annual votes to stay organized.

In exchange for bearing more costs and losing bargaining leverage, public employees were promised no furloughs or layoffs. Walker has threatened to order layoffs of up to 6,000 state workers if the measure does not pass.

Associated Press writers Todd Richmond and Jason Smathers in Madison and Sean Murphy in Oklahoma City contributed to this story.