If the British government goes ahead with its unilateral plan to change the Northern Ireland Protocol, the implications for Northern Irish dairy farmers would be severe.
At the moment, because of the protocol, the island of Ireland is treated as one epidemiological region and Northern Ireland dairy farmers can seamlessly sell milk to the south.
They can equally sell milk to the rest of the UK and, according to Dairy Council Northern Ireland, it is an ideal world.
"We have made it clear to the UK government and the EU that the protocol is working and it's allowing our trade flows to continue," said Dr Mike Johnston CEO of DCNI.
"Is it perfect? No. Are there things that would benefit if they were fixed? Yes, but don't throw out the baby with the bath water," Dr Johnston said.
At the moment, 800 million litres of milk from Northern Ireland is transported south every year for processing into dairy products, such as cheese, butter, infant formula and milk powder. Another 100 million litres is sold in Ireland as liquid milk in shops.
The fear for Northern Irish dairy farmers is that this would all be stopped if the UK decides to introduce its own food standards by replacing the protocol and diverging from EU standards.
"We've had a look over that cliff edge on a couple of occasions," Mr Johnston said.
"I have to tell you, it was not pretty to look over. It would have meant the movement of raw milk from NI to the Republic for processing would have been so difficult as to render it impossible.
"The problem then is one of processing capacity, because we don't have the capacity in NI to deal with all the milk we produce."
From a southern point of view, the loss of such a large amount of milk would cause market upheaval and complications for processors.
First, there would be the loss of liquid milk in shops and supermarkets, as one in four litres comes from Northern Ireland, and then processors would have to review products to make sure there is no Northern Irish milk.
Conor Mulvihill of Dairy Industry Ireland said a milk border would be created.
"The EU would probably not recognise Northern Irish milk as EU single market milk and therefore we have a huge problem," Mr Mulvihill said.
"If the British enact this, those products won't have single market status and, therefore, cannot be exported, unless we can prove it is milk only from the 26 counties. It would be a travesty."
Several sources briefed on the bill say its provisions could have serious implications for the food and drink industry in Northern Ireland and its all-island dimension, but also for the regulatory arrangements for industrial goods.
In particular, the dairy industry could be hit because it relies on UK grain for its feedstocks.
Under a dual regulatory regime, that was not co-designed with the EU, such grain would not be recognised as produced to EU standard and that would therefore put a question mark over the circulation of Northern Irish dairy products in the Republic.
Industry sources say this could put at risk some 800 million litres of milk from Northern Ireland that is processed annually in the south.
It could also put at risk Northern Ireland dairy products that are used as inputs into goods produced in the south and then sold into the EU's single market.
The legislation is expected next week.
