MADISON, Wis. — A bipartisan proposal making it a felony to trespass or damage oil or gas pipelines in Wisconsin is moving through the state Legislature, despite complaints Thursday from opponents that it would violate free speech rights.

The bill heard by a state Assembly committee builds upon a 2015 state law that made it a felony to intentionally trespass or cause damage to the property of an energy provider. The latest proposal expands the definition of energy provider to include oil and gas pipelines, renewable fuel, and chemical and water infrastructure.

Those found guilty could face up to $10,000 in fines and six years in prison.

The Wisconsin measure has broad support from both Republican and Democratic lawmakers, organized labor unions, utilities, the state chamber of commerce and a variety of trade groups representing farmers, restaurants, the paper industry and others.

Supporters downplayed its intent, calling it the fix to an oversight from the earlier law.

Democratic state Rep. Jason Fields, of Milwaukee, is a co-sponsor of the bill and gave a passionate defense of the measure against critics who say it stifles free speech rights and will make it more difficult to combat climate change.

Fields, who is black, said to be effective protesters need to follow the non-violent model set by Martin Luther King, Jr., Mother Theresa, Ghandi and others.

"What I find appalling is somehow we've gotten to the point of making excuses for destruction of property," Fields testified. "I don't like the Ku Klux Klan but I don't have the right or option to go destroy their property. ... I don't care who you are. Destruction of property is a no-no."

Opponents said they weren't advocating for violence, but were concerned that the bill would unnecessarily escalate penalties for activities that are already crimes and possibly ensnare people who didn't realize they were protesting on private property.

"We already have too many people in prison in Wisconsin," said Patricia Hammel, an attorney from Madison who has represented protesters in court. "There's no need for more felonies in Wisconsin."

Rep. Mike Kuglitsch, the Republican chairman of the energy and utilities committee that held a hearing on the bill, tried to assure opponents that only intentionally illegal activity would be chargeable as a felony.

"If it's a lawful protest, no one has anything to worry about," he said.

The bill would have to pass the Senate and Assembly, both controlled by Republicans, and be signed by Democratic Gov. Tony Evers before becoming law.

Nine other states have similar laws, according to Greenpeace, which opposes the legislation.

The laws aren't about preventing violence or sabotage, they're about intimidating anti-pipeline activists in reaction to protests against the Dakota Access pipeline and the Keystone XL pipeline, said Connor Gibson with Greenpeace.

Earlier this month, a federal judge temporarily blocked enforcement of South Dakota laws that were designed to disruptive demonstrations against the Keystone XL pipeline but that opponents argued violated free speech rights.

The South Dakota law in question allowed charges to be brought against demonstrators who engage in "riot boosting," defined in part as encouraging violence during a riot. It was meant to head off Keystone XL protests like those mounted against the Dakota Access pipeline in that state that resulted in 761 arrests over a six-month span beginning in late 2016.

Unlike the South Dakota law, the Wisconsin proposal does not include provisions allowing for fines to be levied against organizations that support protesters.