European Commission spokeswoman Mina Andreeva said "complying with decisions of Court of Justice of the EU is indeed an integral part of European law upon which our very union is founded."
Poland's environment ministry said Monday it would keep logging despite the ban. Polish news channels have broadcast footage of fresh logging this week.
The Bialowieza Forest, one of Europe's last primeval woodlands and a UNESCO World Heritage site, is the subject of a heated political dispute over large-scale logging ordered by Poland's conservative government. Environmentalists and the EU oppose the logging.
The Commission fears the independence of Polish courts could be undermined by new powers granted to the country's justice minister.
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Andreeva said today "if it is confirmed that the logging continues to take place in the Bialowieza Forest, the issue will be taken up in the ongoing rule of law procedure with Poland."
"Poland will have to explain its decision in front of the court," she said.
Younger parts of the forest have been traditionally used to produce some timber, which is a source of income for residents.