The European Union executive said on Thursday that Poland's new law on Russian influence "continues to raise serious concerns."
Despite criticism that it could serve as a tool to persecute political rivals ahead of a national election due this autumn, Poland's President Andrzej Duda - an ally of the ruling Law and Justice (PiS) party - signed the law into force on Wednesday.
The law would, among other things, create a special committee to investigate any undue Russian influence in Poland.
A spokeswoman of the European Commission also said that risked putting Poland at odds with EU laws when the panel starts operating.