An international transport union has called on governments to shun new liability rules while shipper organisations remain at loggerheads over the legislation.

The International Road Transport Union (IRU) said the so-called Rotterdam Rules, which will be officially signed on Wednesday, were a "serious threat to the harmonised application of laws governing the road transport industry".

The president of the IRU commission on legal affairs, Isabelle Bon-Garcin, said: "Under the pretext of standardising maritime law, the Rotterdam Rules dismantle the unity of current laws regulating road transport from the Atlantic to the Pacific, and create an inequity between sea/land transport and land-only transport."

It also believed the new rules conflict with the United Nations convention on the contract for the international carriage of goods by road, and this, said the IRU, would result in "disadvantages" and "confusion".

The union has called on governments not to agree to the new convention, which will come into force as soon as 20 countries have signed-up.

Over recent months, a war of words has erupted between the European Shippers’ Council (ESC), which is against the rules, and US shipper group the National Industrial Transportation League (NITL), which is in favour.

Last week, shipper groups at the Global Shippers’ Forum annual meeting refused to debate the Rotterdam Rules because of continued differences of opinion.

Peter Gatti, executive VP of NITL, said: "The Rotterdam Rules are highly topical and on everyone’s mind, but were not subject to discussion principally because there are general points of disagreement.

"So within the confines of this meeting we’ve agreed to disagree."

ESC secretary general Nicolette van der Jagt said: "There have been exchanges with NITL over the last few months and there are some disagreements.

"We have not been able to reach a common position and that situation did not change during the Global Shippers’ Forum ."

One attendee at the forum said he felt the Rotterdam Rules would be pushed through, as it looked likely the US would sign-up and others would follow suit. -IFW