The head of a Stormont committee has criticised DUP representatives who declined to take part in a meeting on the Northern Ireland Protocol.
The snub came as the Executive Committee heard from Northern Ireland MPs as well as TDs and senators from the Republic of Ireland's Committee on the Implementation of the Good Friday Agreement.
Last week the DUP announced it would stop taking part in north-south activities related to the protocol.
There has been opposition to additional checks at the region's ports under the terms of the protocol, with unionists condemning an "Irish Sea border".
Executive Committee chairman Colin McGrath said he had been informed that members of the DUP would not be attending that segment of the meeting.
"I do have to say that I find that disappointing," he said.
"There are many businesses and many groups who will be impacted by the rollout of the protocol in its early days, and I feel that if you're not prepared to be part of the solution then you stand accused of being part of the problem.
"I think that is both equally unhelpful and is quite sad."
Sinn Féin's Fermanagh MP Michelle Gildernew said it was "unfortunate" that not all parties were represented.
"We have unprecedented challenges on the island of Ireland as a result of Brexit," she said.
The SDLP's South Belfast MP Claire Hanna said: "I regret that there are those in the DUP who are not (here). It's 2021, if people can't participate in a video conference about the pressing political, practical and economic issues of our time..."
Senator Niall Blaney said: "Like others, I am disappointed that the DUP have decided not to partake."
He urged that efforts be made to bring the DUP on board with the engagement.
UUP MLA Doug Beattie, the sole unionist representative in attendance, described the DUP's move as "their decision".
He warned of frictions and instabilities that "cannot be batted away and ignored" and could lead to the "unravelling of a lot of good work over many years by many good people".
"In Northern Ireland we have a fine balance where both communities have a balance as to how we go about our daily lives and we worry about that balance continually and right now, if we had put up a hard border on the island of Ireland, that balance would have been upset. We have put a border in the Irish Sea and that balance has been upset and that will affect north-south co-operation," he said.
"I would plead with you all that we cannot ignore that because that's where we are now."
Ms Hanna responded by thanking Mr Beattie for engaging and agreed that Northern Ireland is a "delicately balanced place, and that equilibrium has certainly been upset by Brexit" but she added the realities of friction in the Irish Sea are "considerably more manageable" than frictions on land across 300 border crossings.
Meanwhile, Sinn Féin MLA Martina Anderson raised documentation at Dublin Port "perhaps taking 24 hours", compared with "four hours" at Belfast, Larne and Warrenpoint ports.
She urged that members "get into solution mode" and "work collectively to sort out this Brexit mess".
"I hope that this is only one of many meetings, that we can have other meetings going forward and that we can start to package solutions," she said.
Speaking outside the meeting, Mr McGrath criticised the DUP for a "childish attitude that serves nobody".
He said they missed an important chance to brief political representatives from across the island, branding it a "wasted opportunity".
