The flow of certain food products into Northern Ireland could be halted if expanded Irish Sea checkpoints are not ready for the end of the Brexit transition period, MLAs have been warned.
Members of Stormont's Infrastructure Committee heard evidence from representatives of the four main ports here - Belfast, Larne, Londonderry and Warrenpoint - about their plans to implement post-Brexit trading arrangements.
A protocol contained in the Brexit Withdrawal Treaty is the arrangement by which Northern Ireland continues to follow single market rules for goods and administers the EU's customs code at its ports.
The Government has acknowledged more regulatory checks will be needed on some goods entering here from Britain, with the expansion of infrastructure to carry out sanitary and phytosanitary (SPS) screening of animals and food products.
But the Government has insisted there will be no new physical customs infrastructure in Northern Ireland.
Yesterday, port bosses gave evidence to MLAs on plans to expand their SPS checking facilities ahead of the end of the transition period at the end of the year.
They voiced concerns about an ongoing lack of certainty about what will be required come January 2021, as proposals contained in the UK Government's command paper on the issue had not yet been agreed by the EU.
MLAs heard that planning permission for new facilities is still required, while there had not yet been any detailed discussions with the Treasury on funding the expansions.
David Holmes, CEO of Warrenpoint Port, was asked by Sinn Fein MLA Liz Kimmins what would happen if the facilities were not ready by the end of the year.
"As it stands, assuming the joint committees (UK-EU) don't move the goalposts and declare that there are less checks required, then there is a potential scenario across Northern Ireland that the food products that require SPS checks won't be able to come in," he said.
"That's in a worst-case scenario."
The ports are working in conjunction with Stormont's Department of Agriculture, Environment and Rural Affairs (DAERA) and HMRC on the requirements for the new checkpoints. Brian McGrath, CEO of Foyle Port, said a hard Brexit could be devastating, with the loss of 40% of trade.
"Instead of being congested, it'll be tumbleweeds we'll be dealing with," he said.
Maurice Bullick, finance and compliance director at the Belfast Harbour Commissioners, said: "We are, I would suggest, very well advanced with DAERA in terms of an in-principle agreement as to how that point-of-entry facility will be structured and how it will operate."
Larne Port boss Roger Armson said it was also "very close" to an agreement to get a "spade in the ground to be ready for January 1".
However, Mr Armson warned that anything that slows the exit of each vehicle from a ferry, even by a number of seconds, could have a disruptive impact on business.