In some cases tariffs will have to be paid, but can be rebated if it can be shown the goods have remained in Northern Ireland.
Some goods, particularly food products, will need to be checked at the port of entry.
Goods going from Northern Ireland to Great Britain will be subject to an exit declaration.
Does this mean there will be checks on goods?
Ministers have insisted this a minor piece of administration, which will not lead to goods being checked.
A joint committee of the UK and EU is supposed to develop the operational processes.
On the current timetable, a new system would have to be up and running by the end of the Brexit ‘transition period’ in December 2020.
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Manufacturing NI said that will not be enough time and the government should commit to extending the transition.
Supermarkets and food wholesalers are likely to face the bulk of new checks on goods coming into Northern Ireland.
‘Government needs to work with us’
The NI Retail Consortium (NIRC), which speaks for major retailers, has welcomed the proposed deal but said a lot of work is now needed.
Aodhan Connolly, director of the NIRC, said business groups had no prior notice on what the deal would amount to.
He said: “Removing the threat of a disastrous no-deal is welcome as is unfettered trade with Ireland and the EU.
“Unfortunately that unfettered access is not the same for goods that enter Northern Ireland from Great Britain and that is a problem.
“If this deal passes in the future we need the government to work with us to mitigate the need for costly checks, declarations and to make any administration as light touch as possible so we can continue to provide Northern Ireland shoppers with choice and affordability.”