Conservative writer Heather Mac Donald, invited to Claremont McKenna College to speak about law enforcement policy in black neighborhoods, addressed an auditorium of less than 20.

Outside the hall, throngs of angry students stood against the door, chanting and linking arms, refusing to let anyone in to hear her speak. With access to the talk blocked, organizers livestreamed her event. Afterward, she slipped out a back door with police escort.

At the University of California-Berkeley, a planned speech by alt-right provocateur Milo Yiannopoulos resulted in broken windows. At Middlebury College, the controversial social scientist Charles Murray was hounded by students as he left his talk early.

And at the University of Wisconsin-Madison in February, conservative commentator Ben Shapiro was interrupted by dozens of students yelling “shame,” as he gave a lecture about safe spaces, free speech and political correctness.

U.S. college campuses have long been a place for debate and public demonstrations, and some worry the push by students to shut down speakers they disagree with is a setback for the free speech protections afforded by the U.S. Constitution.

A legislator in Wisconsin has responded by introducing a bill to punish people who try to shut down these events.

The Campus Free Speech Act would require University of Wisconsin campuses to suspend and expel students who interrupt invited speakers. Representative Jesse Kremer, a Republican and the bill's author, says hecklers should not be allowed to usurp speakers.

“Repeatedly, we've seen students shouted down and silenced by those in disagreement,” Kremer said in a statement. This bill “will end the unconstitutional heckler’s ‘veto’ and create a behavioral shift on campus.”

If voted into law, students would face discipline for taking part in demonstrations that “interfere with the rights of others to engage in or listen” to invited speakers. The bill outlines interferences including, “violent, abusive, indecent, profane, boisterous, obscene, unreasonably loud or disorderly conduct.” A third violation would be grounds for expulsion.

But some legal observers say the proposed bill itself runs afoul of constitutional protections.

“The language in the bill that says a student can be penalized for boisterous conduct … is too broad to meet constitutional muster,” said Lata Nott, executive director of the First Amendment Center at the Newseum Institute in Washington.

John Behling, UW System Board of Regents president, lauded the new legislation as a way to protect speakers like Shapiro. Wisconsin Gov. Scott Walker, who appointed Behling, also voiced support for the bill.

The “Board of Regents strongly believe in the freedom of expression, and we want to do more to ensure every voice is heard,” Behling said in a statement.

Critics argue that the bill will end up stifling free speech on campus.

“It amazes me that Wisconsin Republicans can support a bill aimed at protecting free speech by limiting free speech,” said state Rep. David Crowley, a Democrat from Milwaukee. The bill is “aimed at limiting exposure to different opinions and creating extreme, unwarranted and unnecessary punishments for exercising your right to protest.”

“When you try to protect free expression by limiting free expression, I think the result would be less free expression for everybody,” Nott said.

She said she would advise Walker to not sign the bill.

Republicans defended the bill, drawing a distinction between disruptive behavior and first amendment-protected protest, which they said would not be banned.

The bill is modeled on legislation drafted by the Phoenix-based Goldwater Institute, a right-wing think-tank named after Sen. Barry Goldwater of Arizona who died in 1998.

Colorado, North Carolina, Virginia, Tennessee and Utah have similar laws already on the books curbing campus speech. A number of states are considering similar bills, including Illinois, Michigan, Texas and California.

"The bill is designed to prevent the sorts of belligerent, violent protests we've seen on some college campuses, including Wisconsin," said Jim Manley, a senior attorney at the Goldwater Institute.

He said the legislation strengthens the First Amendment rights of protesters because it does not allow cities or universities to designate specific “free speech zones.”

“The bill is designed to protect free expression broadly for both protesters and invited speakers,” Manley said.

“Disrupting free speech is unconstitutional,” Republican Rep. Dave Murphy said on the assembly floor. “Disruption is not speech. Disruption isn't protest. Disruption is theft. Theft of another person's right to speak and be heard.”

An earlier version of the story incorrectly reported who invited MacDonald to speak. Claremont McKenna College's research institutes, the Rose Institute and the Salvatori Center, invited MacDonald.

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