Sinn Féin, Alliance, the SDLP, and the Green Party have jointly signed a statement
Four of Northern Ireland's main parties have urged the UK Government to keep the North in the single market and customs union after Brexit.
The leaders of Sinn Féin, Alliance, the SDLP, and the Green Party have signed a joint statement.
It comes amid an apparent split in the British government on how to resolve issues around the Irish border.
Michelle O'Neill, Naomi Long, Colum Eastwood and Steven Agnew say that avoiding a hard border is vital to protect "investment, jobs, trade and the hard-won peace".
The statement says: "The political parties in the Northern Ireland Assembly wish to reaffirm our common position that we cannot withstand exclusion from the single market or customs union.
"The protection of the Good Friday Agreement in all of its parts, including North/South and East/West co-operation is critical to maintaining relationships within, and between these islands."
It adds: "The backstop agreed by both the British Government and the EU27 is the bottom line in order to safeguard our political and economic stability now and for the future."
Ulster Unionist Doug Beattie says his party was not approached in relation to the statement.
He said: "They did not come to us to ask us did we want to join in on that statement.
"I'm not sure if they went to the DUP to ask the DUP if they wanted to join in that statement... or the [Traditional Unionist Voice]... or any other unionist party, I have to say."
The statement comes as Northern Ireland remains without an Executive, as the main parties have failed to reach an agreement since last year's Assembly elections.