Lawmakers in more than a dozen states have introduced legislation aimed at curbing large protests, sparking heated debates as high-profile demonstrations greeted President Donald Trump‘s arrival in the White House.

Sponsors and supporters of the bills defend them as a way to prevent riots and protect public safety, while critics call them a threat to First Amendment rights.

That tug-of-war played out in Arizona this week, as Republican leaders on Monday declared a controversial bill dead after criticism that it undermined the Constitutional right to assembly. The bill would have expanded the definition of racketeering to include rioting and allowed protest organizers to be charged for demonstrations that escalated into riots.

“At the end of the day, I think the people need to know we are not about limiting people’s rights,” House Speaker J.D. Mesnard, a Republican, said in an interview with The Arizona Republic on Monday. The Republican-sponsored proposal had passed the state Senate last week. Arizona state Sen. Sonny Borrelli, who sponsored the bill, told the Republic that his goal had been to prevent property damage caused by riots.

Across the country, bills introduced in at least 18 states this year have sought to criminalize some acts of protest and increase penalties for unlawful demonstrations, targeting protests that turn into riots, as well as those that block highways and require extra policing, according to an analysis by the Washington Post. Most of these measures are either still under consideration or have been voted down. These are some of the key issues they address:

Blocking public roadways
Several states — including Georgia, Iowa, Minnesota, South Dakota and Washington — have all considered bills that would increase the penalties for obstructing traffic and blocking highways.

A proposed state law in Tennessee would provide civil immunity to drivers who injure protesters who are blocking traffic on a public road — “if the driver was exercising due care.” Last month, a similar bill failed in North Dakota, where activists camped for months and, at times, marched on highways to protest the Dakota Access Pipeline.

Costs of policing
Minnesota lawmakers are still considering a bill that would allow government agencies to sue protesters for the cost of policing unlawful demonstrations.

Protests in the state turned violent last year over the police killing of Philando Castile during a traffic stop. The incident garnered national attention after Castile’s girlfriend, Diamond Reynolds, livestreamed the aftermath of the shooting.

Protests-turned-riots
As in Arizona, a few proposed state laws have targeted protests that turn violent.

In Oregon — where an anti-Trump protest in November was declared a riot — a proposed law would require community colleges and public universities to expel any student convicted of rioting. The bill is currently in committee.

A Virginia bill proposed an increased penalty for protesters who remain at a riot after being warned to leave. It was defeated in the state Senate earlier this year.

And in North Dakota, four measures inspired by the Dakota Access Pipeline protests were signed into law last week, increasing the penalties for trespassing and rioting and making it a misdemeanor to wear a mask while committing a crime.

Major protest movements in the U.S. have often been met with legislative responses at the state level, said Stanford professor Doug McAdam, author of Deeply Divided: Racial Politics and Social Movements in Postwar America. He drew comparisons between current proposals and legislation in the 1950s and 1960s that sought to curtail participation in the civil rights movement.

“We’re really living in a period of escalating political action on both sides, deepening divisions,” McAdam said. “Talk of proposing such legislation or even the passage of such bills is not likely to put the genie back in the bottle.”

T.V. Reed, an English professor at Washington State University and author of The Art of Protest, said the scope and severity of recent bills differentiate them from earlier legislation.

“In 40 years of studying protest, I have seen nothing like these proposals,” Reed said in an email to TIME. “These kinds of laws would be un-American.”