The UK government has backtracked on a pledge to avoid customs checks on trade crossing the Irish Sea.
Cabinet Office Minister Michael Gove told parliament there would be additional controls on goods moving between Britain and Northern Ireland once the Brexit transition period ends this year.
However, no tariffs would be applied on goods remaining within the UK customs territory, and only the goods destined for Ireland or the rest of the EU would face levies.
The British government detailed its plan in its "Approach to the Northern Ireland Protocol", released on Wednesday.
The UK left the European Union in January and now has until the end of this year to reach an agreement on a new trade deal with the bloc.
The future of the border between Northern Ireland, which is part of the UK, and the Republic of Ireland, which is part of the EU, has long been a sticking point in Brexit talks.
Both sides were keen to keep the border open to keep vital trade flowing and prevent a resurgence of tensions on the island after decades of sectarian and political violence.
Before he was elected prime minister last year, Boris Johnson had even promised businesses in Northern Ireland that there would be no trade barriers in the Irish Sea and no customs declarations to worry about.
"There will be no forms, no checks, no barriers of any kind. You will have unfettered access," Johnson said back in November.
In its latest proposal, the UK said it saw no need for new customs infrastructure in Northern Ireland, but that checks would be made on some goods heading to the province from the mainland.
"There will be no new physical customs infrastructure and we see no need to build any. We will, however, expand some existing entry points for agrifood goods to provide for proportionate additional controls," the paper reads.
It added that the UK would not apply tariffs on goods coming from the UK and bound for Northern Ireland.
"We will not levy tariffs on goods remaining within the UK customs territory. Only those goods ultimately entering Ireland or the rest of the EU, or at clear and substantial risk of doing so, will face tariffs," the paper reads.
Analysis from our political editor, Darren McCaffrey:
"One of the key concerns during Brexit negotiations was trying to ensure that the border in Ireland remains as free and frictionless as it currently is.
"That meant that in many ways that border had to move to the Irish Sea. There were strong objections from unionists in Northern Ireland about the prospect of an internal border between Great Britain and Northern Ireland.
"But it is something that the UK government does seem now to have had to accept – that there will be checks on some goods flowing between Great Britain and Northern Ireland, that there will be extra customs posts and indeed inspections. And that Northern Ireland itself may have to adhere to state aid rules that apply to the rest of the EU.
"Clearly unionists aren’t happy with this, but that is currently where we’re at.
"This was part of a legal draft document positioned by the UK yesterday, which set out essentially what it wants to see in these talks during this transition period.
"It wants to see different deals done at different times with different oversights, on things like fisheries, security, transport and on trade.
"The EU, of course, wants to see an overarching deal with a level-playing field, and it has a special deal for Britain that is not like any other trade deal with other countries because of the UK’s size and close proximity to the EU.”
Watch Darren's report in the video player above.