The DUP has dismissed a suggestion that agri-food trade could be regulated on an all-Ireland basis after Brexit.
Agri-food is a particular challenge to the “no hard border” policy because of strict EU rules on food imports.
An internal European Commission memo seen by Irish broadcaster RTÉ suggested Northern Ireland could effectively remain in the EU system for agri-food.
That would require controls between Northern Ireland and Great Britain, enforced at ports by EU officials.
It would also mean Northern Ireland would have to indefinitely comply with EU animal health and food safety rules.
The memo was passed to the Irish government in February, RTÉ reported.
DUP MEP Diane Dodds said it would be “politically unacceptable and economically catastrophic” to erect trade barriers between Northern Ireland and the rest of the UK.
“It is not going to happen,” she said.
A spokesman for the Department of Agriculture in Dublin said: “We are aware of the document referred to in the story by RTÉ.
“The document has no official status but should be seen as an exploration of ideas on how to address the very serious issues facing the island of Ireland as a result of the UK’s decision to withdraw from the EU.
“The government has been consistent in its view that a political solution is required, especially on the objective of avoiding a hard border, and that technical solutions should not be the starting point.”
A spokesman for the Department of Agriculture, Environment and Rural Affairs said: “DAERA has not seen the paper and therefore cannot give a view at this stage.”