The European Union on Thursday launched an investigation into Polish logging in its ancient Bialowieza forest, a protected UNESCO World Heritage site which includes some of Europe's last primeval woodland.

"The commission has launched an infringement procedure against Poland... the commission is in contact with the Polish authorities to make sure that any measures are in line with EU law," a spokesman said.

"Polish authorities have one month to provide the information requested and once received, the commission will carefully assess this to decide whether further action is necessary."

The probe comes with Brussels and Warsaw already at loggerheads over changes to Poland's constitutional court which the EU has warned could merit sanctions as a "systemic threat" to the rule of law.

The Bialowieza forest straddles Poland's eastern border with Belarus and is home to unique plant and animal life, including a herd of some 800 European bison, the continent's largest mammal.

The vast woodland includes one of the largest surviving parts of the primeval forest that covered the European plain ten thousand years ago.

The Polish government began logging last month, saying it was clearing dead trees to prevent damage caused by the spruce bark beetle, in line with EU regulations.

Environmentalists argue that the entire Polish part of the forest should be designated as a nature park, meaning logging would be forbidden.

They took their complaint to the European Commission, the EU's executive arm.

The coalition of seven environmental NGOs said Thursday the infringement procedure "could result in Poland being taken to the European Court of Justice for breaching the EU Habitats Directive."

Poland's environment ministry meanwhile denied any wrong-doing, insisting that its Bialowieza policy was entirely legal and in line with EU directives. 

Backed by many Polish scientists, the NGOs insist that large-scale logging and particularly the removal of spruce bark beetle-infested dead wood threaten a multitude of plant and animal species.

"It is estimated that around 50 percent of biodiversity within the Bialowieża Forest is dependent on dead wood," said the groups including ClientEarth, WWF, Greenpeace and Birdlife.