Translation:The citizens are protesting against the law.
Is this sentence saying that the protestors disagree, with a specific law, or that the protest is illegal?
They disagree and thus protest.
If their protest were illegal, you'd say:
Mit ihrem Protest verstoßen die Bürger gegen das Gesetz.
Isn't "townsfolk" an exact translation of "Bürger"? Duo wouldn't take it. I imagine a group of indignant merchants gathered in front of the Rathaus, with the councilors cowering inside.