Poland signed an international copyright agreement on Thursday which fuelled a fourth day of protests by Internet users who say it will lead to online censorship.
Protesters rallied in the cities of Poznan and Lublin after the treaty was signed.
The Anti-Counteriting Trade Agreement, or ACTA, aims to harmonise international standards on intellectual property theft. The agreement takes aim at online piracy of movies and music, and opponents fear it will lead to content being blocked on the Internet.
The treaty shares some similarities with SOPA in the United States, which was delayed by lawmakers after widespread outrage against the move.
Poland was one of several EU countries to sign ACTA on Thursday, including Finland, France, Ireland, Italy, Portugal, Romania and Greece.
The United States, Canada and South Korea signed the treaty last year.
