The Traditional Unionist Voice (TUV) conference has been told that to accept the Windsor Framework is to accept that Northern Ireland would "never again be a full part of the United Kingdom".
TUV leader Jim Allister said the Windsor Framework's formal sign-off on Friday was a "day of shame" for the United Kingdom.
He said Foreign Secretary James Cleverly signed away "British sovereignty over a part of this kingdom" and said it confirmed that Northern Ireland would be "treated like a colony" by being subject to European Union laws.
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Mr Allister added that the Windsor Framework "has not made any change of substance" to the Northern Ireland Protocol.
"Our British country has assented to a legal reality that we are under a customs code that operates on the basis that GB - our biggest market - is a foreign country," he said
Mr Allister described the implementation of EU laws in Northern Ireland as an "obscenity".
"We've become colonial rule takers from our colonial masters in Brussels," he said.
Mr Allister described the so-called Stormont brake as "a fraud, a con, a fake".
"The only MOT the Stormont brake would pass is the 'master of trickery'," he said.
He told conference attendees that accepting the Windsor Framework could put Northern Ireland on a trajectory to Irish unity.
"That is the evil genius and intent of the protocol and the Windsor Framework," he added.
Mr Allister criticised the DUP panel on the Windsor Framework, adding that no unionist leader should need to consult "on the acceptability of such hostile annexation".
He criticised Prime Minister Rishi Sunak's characterisation of Northern Ireland's access to the EU market as a positive.
"Strange though, it was the very same EU single market that he didn't want access to for his constituents, because he wanted them to leave the EU," he said.
Also speaking at the conference, former Brexit Party and Reform UK MEP Ben Habib told TUV supporters that the Windsor Framework is "worse than the Northern Ireland Protocol".
"The reason it's worse than the protocol is because it imbeds indelibly EU laws in Northern Ireland," he said.
He said it was an "abomination" that the EU could see internal trading data between Great Britain and Northern Ireland
He added: "The establishment had already decided and accepted the price for Brexit is Northern Ireland and were prepared to throw Northern Ireland under the bus."
Mr Habib, who previously took a Supreme Court challenge against the protocol, said his aim was to "obliterate the Tory Party" and he encouraged unionists to "make a stand against Westminster on the mainland".
Mr Allister warned that returning to Stormont had the "unavoidable price" of becoming "protocol slaves".
He added that there was "another price" to returning to Stormont: "To accept the Windsor Framework, you also accept the booby prize of a Sinn Fein first minister."
He said unionism would "be better without" Stormont than to participate with a Sinn Fein first minister.
Mr Allister said voters should "inject strength into the body politic of unionism" by voting for the TUV during local elections on May 18.
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