DUP leader Arlene Foster has insisted "these are significant days for Northern Ireland" as Brexit negotiations intensify.
Speaking after three days of talks with representatives of other European Union countries, Mrs Foster said decisions made by the British government and the Commons in the coming weeks "will be critical".
And she again rejected any suggestion the north should remain within the single market, accusing Brussels of wanting to "place an effective one-way turnstile from Northern Ireland into the rest of the United Kingdom".
"Trade from Great Britain into Northern Ireland would be in danger of restriction," she said.
"Indeed, Northern Ireland's access to any new United Kingdom trade deals would also be regulated by Brussels.
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"That is not the best of both worlds. That is the worst of one world.
"The Prime Minister is a unionist. Many of her cabinet colleagues have assured me of their unionism. Therefore, they could not in good conscience recommend a deal which places a trade barrier on United Kingdom businesses moving goods from one part of the Kingdom to another."
Her comments come a week after she warned the DUP's Brexit "red line" against a deal that would divide Northern Ireland from the rest of the United Kingdom was "blood red".
"There cannot be a border down the Irish Sea, a differential between Northern Ireland and the rest of the UK," she said.
Mrs Foster spoke yesterday following suggestions goods moving from Britain to Northern Ireland could be checked at Dublin Port to avoid a hard border.
The Irish government wants a 'backstop' which would effectively keep the north within the single market and prevent customs checks at the border in the event of a no deal Brexit.
However, goods moving between Britain and the north would still have to be checked because, due to an open border between Northern Ireland and the Republic, they would be able to circulate throughout the European Union.
The 'backstop' plan has been rejected by the British Government and the DUP.
However, RTÉ reported that checks at Dublin Port are being considered as part of EU efforts to "de-dramatise" backstop proposals.
The checks would mean goods from Britain to the north would be checked at Dublin Port before moving northwards.
"What de-dramatisation tries to do is to recognise the nature and type of trade that happens between GB and NI, and to find ways of minimising any checks and controls that would need to be put on that trade," one source told RTÉ.
However, the proposal could have an effect on ports in the north, including Belfast, Larne and Warrenpoint.
More than 80% of Warrenpoint Port's trade is to and from Britain.
Port of Larne is a subsidiary of P&O Ferries.
Dan Bridgett from P&O said: "As long as there are goods and people travelling between the UK and Europe, P&O Ferries will continue to provide a comprehensive ferry and logistics service to and from the continent.
"We will continue to monitor the negotiations between the UK and EU very closely."
Proposals being considered by the EU also include a dual certification system which would allow goods produced in Northern Ireland to circulate freely in Britain and the European Union.
The EU's chief negotiator Michel Barnier outlined other 'de-dramatisation' proposals to the European Parliament this week.
These included allowing companies in Britain to fill in their customs declarations in advance online when shipping to Northern Ireland.
Mr Barnier told the Parliament: "Our proposal gives Northern Ireland benefits that no part of a third country enjoys. In particular, continued access to the single market for goods, and continued benefits from EU free trade agreements."
