Jacquelyn Martin, Associated Press
United Auto Workers union President Bob King applauds at the 2012 UAW National Community Action Program Conference, in Washington, Thursday, March 1, 2012.

LANSING, Mich. — A labor union coalition officially launched a broad campaign Tuesday aimed at protecting collective bargaining rights and pre-empting a possible "right-to-work" movement by Michigan Republicans.

Unions want to present the proposed constitutional amendment to voters in November. To do that, supporters would have to collect at least 322,609 valid voter signatures.

The unions' "Protect Our Jobs" campaign was launched less than a week after United Auto Workers President Bob King said a Michigan coalition had agreed to mount a petition drive aimed at preventing lawmakers from adopting right-to-work laws.

Right-to-work laws generally prohibit labor contracts that require workers to pay union representation fees, and debate has intensified in Michigan in part because Indiana recently became the first Rust Belt state to adopt such a measure.

Republicans hold the majority in the Michigan Legislature. Some of them support right-to-work laws, and House Speaker Jase Bolger leans toward supporting a proposal. But Republican Gov. Rick Snyder has said he doesn't want a right-to-work measure sent to his desk and Republican Senate Majority Leader Randy Richardville said he doesn't think such a bill would pass in the Senate.

"At this point in time, we've just got way too many other priorities that we're working on," Richardville said Tuesday.

Leaders of the union campaign say their ballot proposal goes beyond the right-to-work issue. It potentially could affect a slew of other bills that Michigan lawmakers already have or soon could pass related to collective bargaining rights.

"What this does is it enshrines collective bargaining in the constitution and it gives protections to middle class families and people around the state from those attacks," said Todd Cook of We Are the People, a coalition supported by labor unions.