Northern Ireland's Democratic Unionist Party (DUP) is launching a legal challenge against the Brexit deal's Northern Ireland Protocol.
The party argued in a statement on Sunday evening that the Protocol violates two British laws: The Act of the Union, which guarantees unfettered trade between Great Britain and Northern Ireland; and the Belfast Agreement.
"Neither the Northern Ireland Assembly, the Northern Ireland Executive nor the people of Northern Ireland consented to the Protocol being put in place or the flow of goods from Great Britain to Northern Ireland being impeded by checks," DUP leader Arlene Foster said.
"They certainly did not consent to the arrangements for those checks being determined by a power over which we have no democratic say," she added.
Three other unionist figures — Ben Habib, Kate Hoey and Jim Allister — are joining the DUP in its challenge with the party stating that it expects "others will also join this path".
The Northern Ireland Protocol is a key Brexit text that ensures that no hard border is erected between Northern Ireland — a British province — and the Republic of Ireland, an EU member state. Negotiators on both sides of the table feared that a physical barrier between the two territories would endanger the 1998 Good Friday Agreement which put an end to more than three decades of bloody sectarian violence.
The Protocol allows for goods to move freely between Northern Ireland and the Republic of Ireland but customs and veterinary checks are carried out for goods moving between Northern Ireland and Great Britain. British politicians, including Prime Minister Boris Johnson, have criticised the Protocol, which they say creates a de-facto border in the Irish Sea between Northern Ireland and the rest of the UK.
The Protocol has been operational since January 1, after the UK's divorce from the EU was finalised, and is meant to remain in use until another solution can be found.
Some disruption to commerce have been reported following the implementation of the Protocol and earlier this month, checks at some ports were briefly suspended because of concerns over staff safety — graffiti in Larne, some 30 kilometres northeast of Belfast, referred to post-Brexit tensions over Northern Ireland and described port staff as "targets".
The DUP presented a five-point plan against the Protocol in early February which plans for the party to oppose all measures related to the treaty in the Northern Assembly Assembly, to send a "strong signal" to Dublin that the relationships between the two sides of the island are being impacted and to launch a parliamentary petition urging the UK government to trigger Article 16 of the Protocol.
The article allows for either side to unilaterally take action if they judge that the application of the Protocol gives rise to "serious economic, societal or environmental difficulties that are liable to persist, or to diversion of trade."
The petition, which has gathered more than 142,000 signatures is to be debated by MPs in Westminster on Monday.