The chief executive of the Newry and Mourne Enterprise Agency has accused the First Minister Arlene Foster of treating the all-island forum on Brexit with disdain.
Doctor Conor Patterson told the BBC's Inside Business programme that it was the wrong approach to take.
"I was there, others were there, we weren't grandstanding," he said.
"We were there because we're concerned about the future of Northern Ireland and the first minister is first minister for all of Northern Ireland, all its geography and all its people and all its businesses and it's important now that she engages and this disdainful attitude, deriding people, this has to stop."
A spokesperson for the DUP said the party is "already engaged in talks with the Irish government and see no worth in attending talking shops, but engaging directly in negotiations and making our voice heard".
Mrs Foster had previously criticised the Irish government's all-island forum on Brexit.
She described it as a "grandstanding exercise" and said she had better things to do than be a "lone voice among remoaners".
The forum was established in the wake of the EU referendum result.
Taoiseach Enda Kenny said the aim of the All Island Civic Dialogue on Brexit, which took place at the Royal Hospital in Kilmainham on Thursday, was to map out the challenges posed by by the UK's decision to leave the European Union and assess its potential impact on different parts of society.
Although the DUP and UUP did not attend, members from Sinn Féin, the SDLP and the Alliance Party did.
They were joined by representatives from business and farming organisations, as well as civic society.
You can listen to the interview in full on Inside Business on BBC Radio Ulster at 13:30 GMT on Sunday.