Theresa May’s Brexit deal does not breach the Good Friday peace agreement, according to legal advice received by the government.
The government has published a summary of the advice after facing pressure from all parties in Parliament.
Some unionists argue the prime minister’s deal with the EU would amount to a breach of the agreement.
The government paper says the deal does not “affect the principle of consent or any other provision… in any way”.
Five days of debate on the proposed Brexit deal will get under way in the House of Commons on Tuesday, with the prime minister facing the fight of her political life to get MPs to back the deal in a vote on 11 December.
Boris Johnson, who resigned from government over the PM’s Brexit vision, described the withdrawal agreement arrangement in his weekly Daily Telegraph column as “a great steel trap that is about to clamp its jaws around our hind limbs and prevent our escape”.
The DUP’s Sammy Wilson said it was important for MPs to know exactly what they are voting for and the implications for Northern Ireland.
Sinn Féin’s Michelle O’Neill said the backstop contained in the EU withdrawal agreement is the only way to protect the 1998 Good Friday Agreement.
She insisted that was the case whatever decision Parliament took on the publication of government legal advice.
The government has resisted demands that advice offered by the attorney general on Brexit be made public.
SDLP leader Colum Eastwood said that whatever the legal advice, Brexit remained a terrible idea.
He added it was reckless for anyone to maintain there was an alternative to the backstop.
Alliance Party deputy leader Stephen Farry and Green Party leader Clare Bailey also argued that the backstop must be protected as the minimum required to protect the interests of people in Northern Ireland.
The politicians were speaking after meeting a number of civic groups at Stormont.
Labour has warned that the UK faces a “constitutional crisis” if Theresa May does not publish the full legal advice on her Brexit.
The prime minister has said the advice is confidential but some MPs think ministers do not want to admit it says the UK could be indefinitely tied to EU customs rules.
MPs say this will not not respect a binding Commons vote last month, which required the government to lay before Parliament “any legal advice in full”.