Boris Johnson has been warned that loyalists in Northern Ireland will “not tolerate an economic united Ireland”.
The warning came as a host of loyalists gathered for a meeting at the Constitutional Club in east Belfast.
DUP councillor George Dorrian was among those who attended.
Loyalist spokesman Jamie Bryson said there is “immense anger” within loyalism around the current proposed Brexit deal.
Proposals agreed by Boris Johnson and the EU cannot come into force until they are approved by both Westminster and the European Parliament.
The DUP has criticised current proposals, arguing they will put a legal, customs and economic border down the Irish Sea.
It is also opposed to the proposed consent mechanism, which would give the Assembly a say on whether or not to continue following EU customs rules, but would not give the DUP a veto.
A pamphlet advertising tonight’s event described the British Prime Minister’s deal as the “betrayal act”.
Speaking to media after the meeting concluded, Mr Bryson said: “The unionist and loyalist community have had enough of this one-sided peace process, we’re not going to tolerate an economic united Ireland and that was the feeling in the room.
“The anger is immense across unionism and loyalism, I can’t think of a section of unionism or loyalism who was not represented here tonight in east Belfast so when you ask what was the outcome, no one group was behind this, it’s not one group to come up with an outcome, this was the people speaking, this was the unionist and loyalist people speaking.
“They can take that message back to Boris Johnson. For three years Leo Varadkar and the Irish Government went to the European Parliament and everywhere else and said we can’t have a border on the island of Ireland because it’s a threat to peace, but it’s OK we’ll just shaft the loyalists and put a border in the Irish sea.
“I think they are entering very dangerous territory at this point in time.”
He added: “The message to the DUP is to stand firm, there was DUP representatives in the room tonight, they will have heard the anger from right across the unionist and loyalist community.”
When asked whether he was “stoking up violence”, Mr Bryson responded: “No one is trying to stoke up violence, but let me say this, it is good enough for the IRA, it’s good enough for nationalism including the Irish Government to win concessions and drive us into an economic united Ireland.
“No sensible person wants to see violence, loyalism has spent three years reaffirming a commitment to peace, but ultimately loyalism’s support for the peace process and the Belfast Agreement was predicated upon one very simple thing, the union is safe and the threat of violence has been used to undermine the union and drive us into an economic united Ireland and people can read into that whatever way they want.”