At least 10,000 trees have been felled in the ancient forest, which is a Unesco World Heritage Site nourishing plenty of animals and plants, including Europe's largest herd of bison, Xinhua news agency reported.
A minimum fine of 4.3 million euros (about $5.3 million) could be levied against Poland unless the tree felling is stopped, the court ruled on Tuesday.
"If they comply with the judgment, no problem. If they don't, we have a possibility to go to a second infringement procedure that may end up in fines," a European Union official said on Tuesday.
Unesco has classified the forest nestled across Poland and Belarus on the watershed of the Baltic and Black Seas as a site of "outstanding universal value".
Poland argued that its decision to increase logging was necessary to combat a beetle infestation.
But the ECJ found that Poland's own documents showed logging posed a greater threat to Bialowieza's integrity.
The ECJ ruling was hailed by environmental activists.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
