Farmers have said it is impossible to see how the Irish border can stay open and free of checkpoints under the Brexit proposals.
While the Ulster Farmers' Union (UFU) warned thousands of jobs are at risk in Northern Ireland, the Irish Farmers' Association (IFA) in the Republic said the UK Government will have to make more compromises on its ambitious international trade targets.
Some 40% of the exports south of the border are destined for a UK market.
In Northern Ireland, more than 50% of agri-food produce goes to the Republic, and it is valued at more than €750m (£683m).
As London published its border and customs proposals for Brexit, the IFA said it was difficult to see how goods and people could continue to move freely north and south if the UK operates an independent customs and trade policy separate to the European Union.