BRUSSELS (Reuters) - Poland, Bulgaria and other eastern European Union states are mulling a legal challenge to new road transport rules that would force their trucks to return home every eight weeks, a change they say would harm their trucking companies, diplomats said.

The overhaul of trucking rules is promoted by their wealthier peers, including France and the Netherlands, and the dispute cuts to the core of the east-west divisions undermining the bloc’s unity that has already been tarnished by Brexit.

Poorer countries on the EU’s eastern flank want to benefit by offering services at lower prices to expand their economies and catch up on growth after decades behind the Iron Curtain.

Their lorries and drivers criss-crossing the EU, France and others worry that the practice undercuts their own workers.

Most EU countries agreed last December to reform the EU’s road transport sector, including to give truck drivers working abroad the right to return home every three to four weeks, stipulating that their weekly rest of at least 45 hours must be spent outside of the vehicle and not in parking areas, and that employers must pay for accommodation.

The new laws would also force trucks involved in international transport to go back to their company’s headquarters every eight weeks, a move designed to fight against a practice of registering transport firms in countries with lower taxes without actually running their operations there.

But Bulgaria, Romania, Poland, Hungary, Latvia, Lithuania, Estonia, Malta and Cyprus were against, according to diplomatic sources. They want changes to the new rules, which are expected to be discussed by the European Parliament in coming months.

“A group of like-minded countries needs to see changes to this eight-week rule. We shall see how further talks go, or else may be forced to challenge that in the courts,” a senior EU diplomat told Reuters this week.

“It undercuts our companies heavily. If we have no other choice, we will sue at the European Court of Justice,” said a second diplomat from the vexed countries, referring to the EU’s top court.

The easterners say returning empty trucks is economically damaging for their companies, as well as leaving a heavy carbon footprint at a time when the bloc is seeking to curb greenhouse gas emissions to help combat climate change.

The westerners, on the other hand, see current practices in the road transport sector as social dumping - the practice of moving operations to countries with lower wages, taxes or workers’ rights.