LANSING, Mich. — Michigan lawmakers approved bills to prohibit mandatory union dues in workplaces as thousands of chanting protesters thronged the Lansing Capitol.

“This is the day when Michigan freed its workers,” Rep. Lisa Posthumus Lyons, R, said Tuesday during debate on two bills, one for public employees and another for private ones.

If Gov. Rick Snyder, R, signs the so-called right to work measures as promised, Michigan would become the 24th state to enact such legislation, and the second this year after Indiana. The change would be a practical and symbolic rout in a stronghold of organized labor in the United States, and opponents said it presaged political warfare.

“There will be blood,” Rep. Douglas Geiss, D, said in debate.

Bundled-up labor supporters converged on the statehouse as lawmakers debated the measures for the state that’s home to the United Auto Workers and the three largest U.S. automakers. Supporters and opponents clashed, with protesters tearing down a tent set up by Americans for Prosperity, overturning tables and stamping on signs. Police on foot and horseback charged through the crowd, pushing them back with batons.

UAW member Bill Bagwell, 55, from Westland, said the measure would create friction at his General Motors Co. plant in Ypsilanti. Members who pay union dues would detest those who enjoy the benefits of the contract but don’t contribute, he said.

“It’ll create civil war,” Bagwell said.

Officials spent days gearing up for crowds brought out by the legislature’s sudden action last week to give initial approval to the anti-dues bills, which exclude police and firefighters.

The crowd numbered more than 10,000, according to State Police Inspector Gene Adamczyk, with more buses still arriving. The Capitol was closed when it reached its capacity of 2,000.

In Wisconsin, which passed restrictions on government-worker unions last year, protests drew as many as 60,000.

Michigan’s push for the laws began last week, when Snyder ended more than a year of neutrality and declared he would sign the legislation. Hours later, it won initial approval in the House of Representatives and Senate with no hearings.

Democrats failed to strip from the bills a $1 million appropriation to administer the measures. The inclusion of the money will shield the laws from a public referendum to repeal them.

“This is being shoved down middle-class families’ throats,” Rep. Jon Switalski, D, said during the debate.

Supporters say right-to-work laws give workers the option of not supporting unions they view as ineffective or politically at odds with them.

“We are empowering families and workers, and allowing them to take control of their own lives,” said Rep. Greg MacMaster, R.

Earlier Tuesday, Americans for Prosperity, an organization supported by billionaires Charles and David Koch, ceded the steps of the Capitol, which they had reserved, due to safety concerns and retreated to the tent, said Annie Patnaude, deputy state director.

Private security officers hired by the organization kept opponents out before the tent went down, and shouting matches erupted. Opponents tore down signs with slogans such as “Stop feeding the union pigs.”

The dues issue came to a head after unions spent $23 million in an unsuccessful campaign to enshrine collective- bargaining rights in the state constitution with a ballot measure in November. Snyder had asked union leaders not to seek the constitutional amendment, and he campaigned against it, saying it would undo efforts to rein in employee costs.

President Obama, who was the beneficiary of union contributions in his re-election campaign this year, said Sunday in a visit to Michigan that “we don’t want a race to the bottom.”

“What they’re really talking about is giving you the right to work for less money,” Obama told workers at the Detroit Diesel plant.

The events in Michigan, with a history of combative organizing and powerful ties to the UAW and International Brotherhood of Teamsters, are watched by unions as a possible harbinger of similar campaigns in other states. Opponents say the laws are an attempt to strip unions of money used not only to bargain with management but to support political campaigns.

About 17 percent of Michigan’s work force belongs to unions, according to the Department of Labor. In the early 1960s, about 40 percent did.