Hundreds marched in Warsaw on Saturday to protest widespread logging in Europe’s last primeval forest, a project undertaken by Poland’s conservative government.

The ruling Law and Justice party has allowed increased logging in the Bialowieza Forest, a vast woodland that straddles Poland and Belarus, alarming environmentalists who say it threatens a natural treasure. The forest has been designated a UNESCO World Heritage site.

The government says it has increased logging to fight an outbreak of bark beetle, which has infected many spruce trees. But ecologists see that as a pretext to increase timber production for profit, saying authorities have been felling not only infected trees but also healthy ones, some 100 years old. Young trees are to be planted in their place.

Speakers at the rally organized by Greenpeace and other groups said they want the entire forest to be declared a national park to ensure its protection. They fear the virgin forest, home to a complex ecosystem of bison, woodpeckers and many other species, is being transformed into what will be essentially a tree plantation.

Robert Cyglicki, director of Greenpeace in Poland, called the logging “a crime against our heritage.”

Protesters rallied in central Warsaw and then marched to the Environment Ministry.

Currently only the forest’s core is protected as a national park on the Polish side.

The march came several days after Environment Minister Jan Szyszko called for Bialowieza to lose its UNESCO natural heritage status.

“The Bialowieza forest was granted UNESCO natural heritage status illegally and without consulting the local community,” Szyszko said. He said a complaint was lodged with prosecutors over the decision, which occurred under a previous government.

Last year he approved a decision to triple logging above a level that had been considered environmentally sustainable.

The European Union says the increased logging is illegal under EU law.

In recent days, protesters have sought to stop logging in the forest, at times by trying to block the heavy equipment.