The bypasses are to form sections of the Via Baltica – or European route E67 - which is part of an international highway system linking Warsaw with Helsinki via the Baltic states.

Brussels and green groups argue that the construction of the two roads through the Rospuda Valley would damage important nature sites, which are home to the world's only population of aquatic warblers, as well as rare eagles, lynx, wolves and wild orchids.

They argue that economically viable and less-damaging alternative routes exist to satisfy Poland's need for better infrastructure.

It was understood in a court hearing that construction of the bypasses would remain idle while the court case was pending, said commission spokeswoman Barbara Helfferich. But because Warsaw has failed to debunk press reports saying that work will resume on Wednesday (1 August), Brussels has asked the ECJ to issue an injunction to "prevent irreversible damage to a unique natural site."

"If this request is accepted, the court will issue an order asking Poland not to go ahead with the construction of the by-passes through the Rospuda Valley while the case is pending."

"We do expect Poland to respect whatever order the court will issue – we cannot imagine that Poland would disregard an order by the European Court of Justice," said Ms Helfferich, who added that if Poland would do so the situation would be unprecedented.

"Never has a member state disregarded interim measures by the European Court of Justice," she told journalists in Brussels.

The Polish government said last week that it halted work for the bird-nesting season but planned to resume construction on Wednesday. Warsaw argues that environmental damage would be minimal, because the plan is for a viaduct and not a road at ground level.

"It is regrettable that Poland has now decided to go ahead with the construction of a new road through Rospuda Valley," EU environment commissioner Stavros Dimas said in a statement on Monday.

"I would hope that Poland will reconsider its decision before irreparable damage is done," he added.

Demonstrations for and against

In Poland, demonstrations by green groups and environmentalists have increased over the weekend with Greenpeace Poland warning that if the road building through the Rospuda Valley commences on Wednesday, hordes of people will come to the valley "to defend its wealth and to prevent the violation of Polish and European law."

"The arrogance of the Polish government towards European law and legal institutions – namely the European Court of Justice – is appalling," said Magda Stoczkiewicz from CEE Bankwatch – an NGO seeking to prevent the environmentally and socially harmful impacts of international development finance.

"Still, we believe that due to the European Commission's reaction, devastation of the unique Rospuda Valley will be halted," she said in a statement on Monday.

However, residents of Augustow, which currently sees some 4000 lorries passing through the town centre each day, have staged a demonstration in favour of the E67 route in support of commencing the Via Baltica works.