They have a right to protest, they don't have a right to honk their horns to cause a nuisance (disturbing the peace) or the right to illegally park in the middle of public streets.
Blackmail using public infrastructure isn't a legal protest tactic. Protest is speech, it's not a license to do whatever you want and break the law.
You just described everything that they’re doing…. It’s not a protest at all.