More then 50 businesses in Northern Ireland have sent an open letter to British MPs warning that a "no deal" Brexit would cause "significant damage" to the region's economy.
Crashing out of the European Union without a deal would affect "export markets, supply chains, consumer spending power and the region's competitiveness," companies including insurance giant Allianz and Bombardier Aerospace wrote.
"The negative economic impact is already starting to bite in terms of the private sector's ability to invest," they said.
Britain is due to leave the bloc on March 29, but London has yet to work out a deal with Brussels palatable to British MPs, with the "backstop" arrangement designed to avoid a hard Irish border the main sticking point.
Critics of the arrangement, which would see Britain remain in the EU's customs union until a future relationship has been worked out, fear it could lock Britain into a close relationship with the EU that it cannot unilaterally end.
But Northern Irish MPs also object to a proposal that could see just Northern Ireland remain in the customs union, while all sides want to avoid a hard border due to fears it could undermine the 1998 Good Friday peace agreement.
"The peace and economic progress that flowed from the Belfast/Good Friday Agreement cannot be overlooked at this critical time in the UK's history," the businesses wrote.
"All members of parliament must consider the burden of responsibility that they now carry for this region's future."