A crowdfunding appeal has been launched for a legal challenge against the Northern Ireland Protocol.
DUP leader Arlene Foster and other unionists from across the UK are proposing judicial review proceedings unless alternative post-Brexit trade arrangements are put in place which secure their consent.
The protocol sees Northern Ireland follow a number of EU trade rules which has necessitated additional checks on goods arriving from Great Britain.
Unionists have criticised the disruption and dubbed the mechanism a border in the Irish Sea.
In a statement on Thursday, campaigners said legal proceedings to end the protocol have been commenced by a “wide coalition of pro-unionists”.
A full hearing at the High Court in Northern Ireland is expected in May.
Mrs Foster tweeted that the crowdfunding appeal is an opportunity for all who oppose the protocol to “play their part”.
“We cannot allow our United Kingdom to be ripped apart and our UK internal market to be divided in order to protect the single market of the EU,” she wrote.
“When I launched a petition calling for unfettered GB-NI trade, over 100k people joined with us in just over 24hrs, this is another opportunity for everyone who opposes the Protocol to play their part.
“We will work with other Unionists to send a united message to our Government and to free Northern Ireland from the Protocol.
“Whilst the courts is one front in this fight, the UK Government must use all powers at its disposal to immediately remove any barriers to unfettered trade within the United Kingdom.”
UUP leader Steve Aiken said the protocol “fundamentally undermines the integrity of the United Kingdom, the Belfast Agreement and the principle of consent”.
“As one of the parties that negotiated the agreement, we believe we have to take every political, diplomatic and legal avenue open to us to see the invidious, unequal NI Protocol annulled, because every day we see the very principles on which the Belfast Agreement was created being trampled on by those who claim to put the peace process at the centre of their arguments,” he said.
“We encourage everyone who believes in the Union and in the Belfast Agreement to support this legal case.”
TUV leader Jim Allister said: “The protocol annexes Northern Ireland into the EU, leaving us subject to laws we did not make and cannot change.
“For me the challenge and opportunity of this judicial review is to end such vassalage and reunify the United Kingdom by removing the constitutional threat of many of our laws not being made in Belfast or London, but in Brussels under foreign aegis and control.
“It is about ‘taking back control’ in a most fundamental way by restoring the key sovereignty principle of being governed only by our own nation’s laws, legislatures and courts.”
The action has also been backed by former first minister Lord Trimble.
“I have joined in these legal proceedings because Northern Ireland’s place as an integral part of the United Kingdom is at stake,” he said.
“Extensive parts of Northern Ireland – much of its economic fabric – have been turned into a colony of the European Union.
“We accept that the Government is trying to mitigate and minimise the effects of the protocol, but that is not enough.
“It does not change the fact that the Government is acting contrary to our constitution, and that is why we have concluded that the only way we can deal with it is by taking legal proceedings.”
Ben Habib, chairman of Unlocked and former London MEP, said: “We must not rest until the protocol is ended. It is vital that all pro-unionists join together in this fight.”