The Progressive Unionist Party has warned that loyalist support for the Good Friday Agreement could be withdrawn, due to changes to the treaty's cross community support mechanism to facilitate Brexit.
Party leader Billy Hutchinson has accused Secretary of State Brandon Lewis of the "unilateral amending of Northern Ireland Act" in order to allow the Brexit protocol to be implemented.
Under the terms of the Withdrawal Agreement, Stormont will be periodically asked to consent to the protocol, giving the assembly an opportunity to remain in the arrangements or choose to exit from them.
However, proposals for the consent mechanism - which under the current timeline would be at the end of 2024 - is by way of a simple majority of MLAs, removing the cross community support mechanism contained in the GFA.
The loyalist leader says "key loyalist support" for the agreement was predicated by elements they claim have been removed.
It comes just days after a delegation from the Loyalist Communities Council held a meeting with the NIO regarding loyalist anger at the Brexit deal, which places a customs border in the Irish Sea.
Brandon Lewis has repeatedly denied the existence of a regulatory border between the north and Britain, despite it being part of the UK-EU Withdrawal Agreement, that goods moving east to west must undergo checks overseen by EU officials at seaports and airports.
"Back before the Belfast Agreement was signed the Progressive Unionist Party took part in explorative discussions with various groups as to how Northern Ireland could move forward positively and how they could support that movement", said Mr Hutchinson.
In relation to the historic 1998 peace treaty he said "A key to loyalist support for the Belfast Agreement were the safeguards contained within Strand 1 (5) (d) as this would enshrine cross community consent working.
"This promise of cross community consent being required for key issues was given effect by Section 42 of the Northern Ireland Act 1998, which put the Belfast Agreement into effect within domestic law.
"Indeed Section 42 of the Northern Ireland explicitly provides that “a matter coming before the Assembly” can be subject to a petition of concern, which is the manner by which the safeguards within Strand 1 (5) (d) was given effect".
The statement from the loyalist political party, which has affiliations with the UVF, appears to echo an argument made by loyalist Jamie Bryson in a book 'Brexit Betrayed' released earlier this month.
Mr Hutchinson added "Since the signing of the agreement we have been lectured repeatedly about the sacrosanct nature of the Belfast Agreement, but on the 10th of December 2020, without any Unionist consent, the Secretary of State unilaterally amended the Northern Ireland Act.
"In this unannounced manoeuvre, Schedule 6A was inserted. This provision at paragraph 18 (5) disapplied Section 42 for the key vote on the Northern Ireland Protocol, thus denying any recourse to the cross community safeguard which should be available in order to override or publically scrutinise the efforts to create an economic United Ireland with a customs border in the realm of the United Kingdom.
"The Progressive Unionist Party find this attempt to circumvent a key safeguard within the Belfast Agreement very disturbing and it also adds further urgency to our call for a Unionist Convention.
"Now more than ever it is time to put country before party", he added.
