Germany and Ireland on Sunday told Britain there was no legal or political justification for Prime Minister Boris Johnson's plan to override parts of the Brexit deal governing trade with Northern Ireland.
The British parliament is considering a new law which would unilaterally change customs arrangements between Britain and Northern Ireland that were initially agreed as part of its exit deal from the European Union.
Britain says the changes are necessary to ease the overly burdensome requirements of the divorce deal, designed to prevent goods flowing into EU member Ireland via British province Northern Ireland. Johnson says the checks are creating tensions that threaten the region's 1998 peace deal.
But, writing in the Observer newspaper foreign ministers from Germany and Ireland rejected that argument.
"There is no legal or political justification for unilaterally breaking an international agreement entered into only two years ago," Germany's Annalena Baerbock and Ireland's Simon Coveney said.
"The tabling of legislation will not fix the challenges around the protocol. Instead, it will create a new set of uncertainties and make it more challenging to find durable solutions."
Johnson's government says its preference remains to find a negotiated solution with the EU, but that Brussels needs to be more flexible to make that possible. The EU says it has put forward a range of possible solutions.
"We urge the British government to step back from their unilateral approach and show the same pragmatism and readiness to compromise the EU has shown," Baerbock and Coveney said.
The legislation, known as the Northern Ireland Protocol Bill, passed its first parliamentary hurdle last week, but is expected to face stiffer tests before it becomes law with many parliamentarians opposed to breaking a treaty obligation.
It is next due to be debated in parliament on 13 July.