The Republic of Ireland would have to build border inspection posts if it wanted to continue importing food from Northern Ireland in the event of a no-deal Brexit, a report has concluded.
The study was commissioned by NI's Department for the Economy.
The EU has strict rules for checking imports of animals and food products at its borders.
Those products must come through inspection posts in the immediate vicinity of the point of entry.
Ireland currently has border inspection posts (BIPS) at Dublin Airport Port, Dublin Port and Shannon Airport.
The report by Eric Pickett and Michael Lux says this is "problematic when considering north-south trade in sensitive goods and products... consequently, Ireland will have to establish BIPS which are closer to the border".
Mr Lux is a former senior official in the tax and customs directorate of the European Commission, while Mr Pickett is a German lawyer specialising in EU customs law.
They note that Switzerland and European Economic Area countries are able to derogate from those strict inspection rules.
However that is because they have a deal with EU so "the problem is that under a no-deal scenario, this option is not available".
The report also suggests that "integrated logistics centres" could be established within 15km of the border to allows customs checks and other inspections to happen in one place.
It also details a range of customs simplification measures which could be taken, such as joint customs offices.
However these would have to be implemented over the long term and would not be in place in the event of a no-deal Brexit later this year.
The report concludes that "many, perhaps most" Northern Ireland small and medium businesses which trade across the border will face significant challenges if the no-deal scenario materialises.
The Irish government has pledged that there will be no new checks or controls at the border even if there is no deal.
However the Taoiseach (Irish prime minister) Leo Varadkar has said food and animal checks will be difficult to get round.
"Customs duties can be collected as other taxes are, either online or into tax offices... When it comes to animal checks it's much more difficult," he said.
"Animal checks can only possibly be done physically by vets."