Protesters held a demonstration at Poland's constitutional court ahead of a crucial ruling that could affect the country's future relationship with the European Union.
Judges are set to decide on Tuesday whether Poland's own constitution has primacy over EU law. Brussels say it doesn't.
On Monday, a small group of activists made it to the court's entrance, as smoke bombs sent black plumes into the air before they were dragged away by police. The demonstrators had brought boards and nails in the hope of nailing the door shut.
Others stood outside the court building with a large banner reading "Civic Shutdown of the ex-Constitutional Tribunal.
Poland’s prime minister had asked the court — dominated by ruling party loyalists — to make the judgment amid a larger conflict over systematic changes to the court system in Poland. The EU has strongly criticised Poland's reforms, viewing them as a violation of democratic norms.
Poland's Constitutional Tribunal was initially expected in April, but this has been postponed.
The pro-democracy activists fear that if the court rules that Polish law has primacy over EU law, it would mark another step away from Western Europe.
Opponents say they do not consider the court legitimate after Poland's ruling conservative party illegally appointed three new judges soon after it won power in 2015.
Human Rights groups have accused Poland's government of tightening its control over the judiciary and media, as well as restricting reproductive rights for women and targeting LGBT people with harsh rhetoric.
The ruling party says its changes to the court, which have been opposed by EU institutions, are meant to fight corruption by judges and make the court system more efficient.
Polish justice minister, Zbigniew Ziobro, said last week that the EU’s criticism amounts to "hybrid warfare" against the Polish legal system.