Will Northern Ireland see a return of The Troubles after the completion of Brexit? At the very least, it appears UK prime minister Boris Johnson and Ireland’s Taoiseach Micheál Martin will get The Headaches. Unionist paramilitary groups have banded together to renounce their support for the Good Friday Agreement after nearly a quarter-century of peach and calm, thanks to the erection of border and trade controls between Northern Ireland and the rest of the UK.

They claim they want peaceful, democratic opposition … for now:

Outlawed Loyalist paramilitary groups in Northern Ireland say they are temporarily withdrawing their support for the historic 1998 peace accord because of the disruption caused by new post-Brexit trade rules.

The groups say they are not planning a return to violence, but the announcement underscores rising tensions over the trade deal agreed between Britain and the European Union days before the U.K. made an economic split from the 27-nation bloc on Dec. 31.

The Loyalist Communities Council, which represents several banned paramilitary groupings, said in a letter to Prime Minister Boris Johnson that the new trade rules undermined the basis of Northern Ireland’s 1998 Good Friday accord, and they would no longer support it until there was “unfettered access for goods, services, and citizens throughout the United Kingdom.”

The letter said opposition to the measures would remain “peaceful and democratic.”

Just how long will that opposition be peaceful and democratic, though? It was a democratic process that pushed Johnson into position where the DUP no longer mattered to the Tory governing majority, at which time Johnson blithely tossed them under the bus to get his divorce deal with the EU. Even Theresa May had refused to erect a quasi-trade border between Northern Ireland and the rest of the UK, although her reliance on DUP was certainly part of that calculation.

Their longer statement threatens to unilaterally end the Good Friday Agreement unless full and unfettered economic access is restored quickly. That doesn’t sound terribly democratic, although it’s not necessarily un-peaceful, so to speak:

“Please do not underestimate the strength of feeling on this issue right across the unionist family … accordingly, I have been instructed to advise you that the loyalist groupings are herewith withdrawing their support for the Belfast agreement until our rights under the agreement are restored and the protocol is amended to ensure unfettered access for goods, services, and citizens throughout the United Kingdom. If you or the EU is not prepared to honour the entirety of the agreement then you will be responsible for the permanent destruction of the agreement.”

John Kyle, a Belfast city councillor with the Progressive Unionist party, which has historical links with the UVF, said there was an “absolute commitment to non-violence” but that the letter’s implications were unclear. “It’s far too early to know how to interpret it. It is premature to assume it means walking away from non-violence.”

That might be more symbolic than substantive, an MP points out. But symbolism married with paramilitary organizations might create a malign substance down the road:

Stephen Farry, an MP with the centrist Alliance party, said loyalist withdrawal from the Good Friday agreement was a political and symbolic gesture. “However, it has no practical consequences. The agreement stands on the basis of the dual referendums in 1998. I am more concerned at the continued escalation of rhetoric and building of unrealistic expectations that the protocol can be replaced in the absence of a plausible alternative.”

Farry added: “It is also concerning that what is essentially a voice for proscribed terrorist organisations is becoming an actor in a political debate.”

This is a reaction to the recent implementation of the final Brexit accord and its follow-on trade agreement. That has resulted in disruptions in the six-county enclave as it bears the brunt of the attempts by both sides to keep the border to the Republic of Ireland open:

Northern Ireland has special status because it shares a border with EU member state Ireland. An open Irish border has helped underpin the peace process built on the Good Friday accord, which ended decades of violence involving Irish republicans, British loyalists and U.K. armed forces, in which more than 3,000 people died.

But the new checks have unsettled the delicate political balance in Northern Ireland, a part of the U.K. where some people identify as British and some as Irish. They are opposed by pro-British Unionists, who say they drive a wedge between Northern Ireland and the rest of the U.K.

Northern Ireland authorities temporarily halted veterinary checks and withdrew border staff from ports last month after threatening graffiti appeared referring to port workers as targets. Police are also investigating threatening graffiti in Belfast referring to Michael Gove, the British government minister responsible for Brexit preparations.

Northern Ireland businesses, meanwhile, say they are struggling to cope with the new red tape. To ease the burden, Britain announced Wednesday it was unilaterally extending until October a temporary “grace period” waiving checks on agri-food goods entering Northern Ireland. It had been due to end March 31.

That drew a rebuke from the EU. European Commission Vice President Maros Šefčovič, joint head of a U.K.-EU committee on Northern Ireland, said it was “a violation” of the legally binding Brexit divorce agreement.

Ireland’s government was also unhappy with the unilateral extension, which Johnson’s government insisted was necessary to head off food shortages in Northern Ireland. Foreign Minister Simon Coveney accused the Brits of being unreliable negotiating partners, which drew a sharp response from DUP leader Arlene Foster:

The North’s First Minister accused the Minister for Foreign Affairs of “ignoring” unionists and called on him to reflect on his language as the political fallout continued on Thursday over the UK’s unilateral decision to extend the grace periods for post-Brexit checks on some goods entering the North from Britain.

Arlene Foster was responding to comments by Simon Coveney, who told RTÉ the EU was “negotiating with a partner that they simply cannot trust.”

Ms Foster said he “talks about not having a partner you can do business with. I have to say, he should reflect on that, because he’s not listening to the unionist people of Northern Ireland. He’s ignoring them, and thinking that they’ll just go away. We will not go away, and we need to be listened to in relation to our very deep concerns.”

In essence, the British and EU negotiators never actually solved the Ireland border issue. All they did was punt it. The eventual agreement — to use Northern Ireland as a checkpoint between the EU and UK — did not erect a border on the island, but instead put one in the Irish Sea and left the unionists adrift. They’re still not Irish, but in trade terms, they’re less British than they used to be. It’s precisely why the DUP refused to allow May to make the agreement that Johnson eventually made to preserve a settled Brexit rather than a crash-out that would have left a hard border in Ireland rather than the virtual one in the Irish Sea.

All of this will end up undermining the Good Friday agreement (known locally more as the Belfast Agreement) in two directions. The unionists will demand a return of the hard border to keep from being separated from the rest of the UK when it comes to trade issues. The republicans will react to that by demanding a vote on reunification, which has gained momentum during the Brexit project as the majority in Northern Ireland wanted to remain part of the EU in the first place. All of this was an entirely predictable outcome from Brexit, and similar issues apply in Scotland, too.

That’s a recipe for violence, and this looks like the first warning of the return of the Troubles all over again. Let’s hope it doesn’t come to that, but layering Brexit on the Good Friday agreement doesn’t leave much room for solutions, if any at all.