There will be "minimal targeted interventions" on trade from Northern Ireland to GB under the PM's Brexit deal, the Brexit secretary has said.
Stephen Barclay's comments came after Northern Ireland business groups appealed for greater clarity about how the deal will affect trade with the rest of the UK.
But how those processes will be implemented is yet to be worked out.
There have been a series of confused, sometimes contradictory, statements by ministers and senior officials on the issue.
Answering an urgent question in the House of Commons on Thursday, Mr Barclay gave details of "exit declarations" which will have to be made on goods going to Great Britain.
Home Office confirms there will be checks on goods between GB and Northern Ireland under Govt deal. @CommonsHomeAffs has just received this memorandum. The Home Secretary couldn’t answer this in committee yesterday pic.twitter.com/2R4Da0bFqx— Yvette Cooper (@YvetteCooperMP) October 24, 2019
He said it would be an electronic form involving "fairly straightforward data".
"This is part of bookings that will be done with the haulier as part of the shipment of goods," he added.
"It actually involves fairly straightforward data in terms of who's exporting, who's importing and what the nature of the goods are."
DUP MP Nigel Dodds said: "This will adversely affect the most important trade we have in Northern Ireland."
He also said Mr Barclay should "waken up and realise" the government was in danger of "causing real problems" with the unionist community.
The president of the business organisation, the CBI, has said "urgent clarity" is needed "from the UK Government about how they intend to protect Northern Ireland's place in the internal market".
Speaking in Belfast, John Allan said: "Northern Ireland businesses simply cannot afford for the next phase of Brexit to drain investment and growth at the level we've seen over the past three years."
Will this result in extra tariffs on goods?
Goods coming into Northern Ireland from elsewhere in the UK will be subject to customs declarations.
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.
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."