LANSING: Michigan Gov. Rick Snyder signed two laws on Tuesday weakening union power, dealing a devastating and once-unthinkable defeat to organised labour in a state that has been a cradle of the labour movement for generations.

The House passed the anti-union bills during the day as hundreds of protesters shouted “shame on you” from the gallery and huge crowds of labour backers massed in the state Capitol halls and on the grounds.

Foes of the laws, including President Barack Obama, were trying to keep the spotlight on this latest battleground in the war over union rights.

Democrats offered a series of amendments, one of which would have allowed a statewide referendum. All were swiftly rejected.

“This is the nuclear option,” Democratic Rep. Doug Geiss. “This is the most divisive issue that we have had to deal with. And this will have repercussions. And it will have personal hard feelings after this is all said and done.”

Once the bills are enacted, it will mark another defeat for the labour movement in the industrial Great Lakes region, known as the Rust Belt for its once-booming manufacturing sector.

Michigan, the centre of the US auto industry, will become the 24th right-to-work state, banning requirements that nonunion employees pay unions for negotiating contracts and other services.

Supporters say the laws give workers more choice and support economic growth, but critics insist the real intent is to weaken organised labour by encouraging workers to “freeload” by withholding money unions need to bargain effectively with management.

“This is about freedom, fairness and equality,” Republican House Speaker Jase Bolger said. “These are basic American rights - rights that should unite us.”

In recent years, legislatures in states like Michigan, Ohio and Wisconsin have been taken over by an aggressive Republican majority that vowed to curtail union rights.

Even with the outcome considered a foregone conclusion, the heated battle showed no sign of cooling as lawmakers prepared to cast final votes.

Hundreds of protesters flooded the state Capitol hours before the House and Senate convened, chanting and whistling in the chilly darkness.