Members of Palikot’s Movement wear masks during a vote of no confidence. (Agencja Gazeta/Reuters)

ACTA is meant to set international standards for violations of intellectual-property laws, but opponents fear it could lead to censorship online. The United States signed the agreement last year, along with Canada and South Korea. For the past week, the agreement has stirred a battle online after the European Union started to consider joining.

On Thursday, Poland and 21 other European Union members signed the treaty. The Internet group Anonymous attacked Polish government Web sites, protesters marched in the streets and lawmakers donned the masks.

There are similarities between ACTA and the recently tabled Stop Online Piracy Act that U.S. Internet companies protested two weeks ago with a blackout.

View Photo Gallery: In Europe, protesters sporting Guy Fawkes masks rally against the Anti-Counterfeiting Trade Agreement with sentiments similar to the anti-SOPA protests in the United States.