Europe’s top court has given Poland 15 days to prove it has complied with a court order to stop logging in Europe’s oldest forest or face fines of €100,000 ($118,000; £89,000) a day.
The European Court of Justice said it was taking action to avoid serious and irreparable damage to the Bialowieza forest, a Unesco World Heritage site.
Poland has not yet commented.
In a controversial decision last year, it approved a threefold increase in logging to combat spruce bark beetle.
The European Commission, which is taking legal action against Poland, has said the logging threatens the habitat of birds and animals, including bison, and can only continue in places where public safety is at risk.
The ECJ said it agreed to the imposition of daily fines because there were grounds to doubt that Poland had complied with its ruling in July to immediately halt the logging.
The European Commission argues that Poland has simply ignored the July court order and large mechanical harvesters have continued to remove trees.
Environmental groups say this is the first time the court has felt the need to impose fines on a country before the case is concluded.
Covers 141,885 hectares (350,606 acres) – mixed forest, but also wetlands and river valleys
17% is protected nature reserve where logging is illegal
Representative of primeval forest that covered most of Europe 10,000 years ago
Home to 59 mammal species (including European bison, lynx, wolf, otter), and more than 250 bird species
Notable for extensive dead wood – habitat for fungi, beetles and worms