More than 20 states have proposed bills that would crack down on protests and demonstrations since Donald Trump was elected, in a moved that UN experts have branded “incompatible with US obligations under international human rights law”.

The proposed laws would variously increase the penalties for protesting in large groups, ban protesters from wearing masks during demonstrations and, in some states, protect drivers from liability if they strike someone taking part in a protest.

The American Civil Liberties Union (ACLU) said more than 30 separate anti-protest bills have been introduced since 8 November in “an unprecedented level of hostility towards protesters in the 21st century”. Their introduction comes amid a huge increase in activism and engagement, much of it inspired by Trump’s election to the presidency.

The ACLU and the National Lawyers Guild have said many of the bills are likely unconstitutional. “The proposed bills have been especially pervasive in states where protests flourished recently,” said Vera Eidelman, who works in the ACLU’s speech, privacy and technology project.

“This flood of bills represents an unprecedented level of hostility towards protesters in the 21st century. And many of these bills attack the right to speak out precisely where the supreme court has historically held it to be the most robust: in public parks, streets and sidewalks.”