Northern Ireland's High Court on Friday issued an interim order suspending a decision by Agriculture Minister Edwin Poots to stop post-Brexit checks on agri-food moving to and from mainland Britain.
The ruling, made by judge Adrian Colton, will stand until a judicial review against the unionist minister's decision can be heard in full.
The checks on trade between the province and mainland Britain are mandated by a post-Brexit EU protocol, but are deeply unpopular among the pro-British community.
Unionist parties say that with checks on the Irish Sea border, to prevent unchecked goods entering the European single market via EU-member Ireland to the south, Northern Ireland risks being cast adrift from the rest of the UK.
The Irish government in Dublin and nationalist, pro-Irish parties in Northern Ireland said the order by Poots, of the Democratic Unionist Party (DUP), broke the law.
In his ruling, Colton said: "There shouldn't be any confusion hanging over those in the Civil Service, so I am persuaded this is a case where there should be interim relief.
"I therefore make the order to suspend the instruction given by the minister for agriculture until further order of this court."
The DUP is bitterly opposed to the Northern Ireland Protocol, an agreement reached between London and Brussels to regulate its trade when the UK left the European Union.
It and all other unionist parties argue the checks on goods coming from England, Scotland and Wales are damaging the Northern Ireland economy.
Irish Foreign Minister Simon Coveney said the threat by Poots amounted to a "breach of international law" and was "a very serious matter indeed".
"It's essentially playing politics with legal obligations. And I certainly hope that it doesn't happen, as has been threatened," he said.
London and Brussels have spent months trying to thrash out compromises to reform the protocol but Poots indicated he wanted to short-circuit the process.
He said his own legal advice stated he had the power to suspend the sanitary checks on plant and animal goods entering Northern Ireland from the UK mainland.
"I have now issued a formal instruction to my permanent secretary to halt all checks that were not in place on December 31, 2020 from midnight tonight," he said on Wednesday.
The DUP is trailing Sinn Fein in opinion polls as Northern Ireland gears up for elections in May, and other parties accuse it of growing increasingly desperate on the question of the protocol.
But the DUP insists that the EU agreement is a threat to Northern Ireland's pro-UK unionist population, and wants London to scrap it unilaterally.
On Thursday, the DUP's Paul Givan resigned as first minister of the power-sharing executive in Belfast, prompting calls from nationalists for early elections.
British Foreign Secretary Liz Truss and EU commission vice president Maros Sefcovic are locked in talks to try to agree changes.
