The UK government may have broken Parliamentary rules by not publishing Brexit legal advice, the Commons Speaker has said.
John Bercow said there was an “arguable case” that a contempt of Parliament has been committed.
It means MPs will debate and vote on the issue on Tuesday.
This is likely to delay the start of the debate on Theresa May’s Brexit deal.
Mr Bercow was responding to a call from senior MPs in six parties – Labour, the Lib Dems, the SNP, the Democratic Unionist Party, Plaid Cymru and the Green Party – for contempt proceedings to be launched.
They say the government has gone back on a binding vote to release “any legal advice in full”.
Attorney General Geoffrey Cox – the government’s chief legal adviser – earlier published an overview of his legal advice on Theresa May’s Brexit deal, and answered MPs’ questions on it.
He argued that it would not be “in the national interest” to publish his advice in full, as it would break a longstanding convention that law officers’ advice to ministers is confidential.
He insisted there was no cover-up, telling MPs: “There is nothing to see here.”
The MPs are also demanding the immediate publication of his final and full legal advice.
MPs are due to vote on Mrs May’s deal on 11 December.
Labour’s shadow Brexit secretary Sir Keir Starmer said: “This is not about party politics.
“It’s about parliamentary democracy and guaranteeing that MPs have the information they need to know – precisely what the government has negotiated with the European Union.
“Even at this 11th hour, I would urge ministers to step back from the brink and to not go down in history as the first government to be found in contempt.”
BBC Newsnight’s political editor Nick Watt said government sources had told him they would not be publishing the legal advice, arguing that to do so would be unprecedented.
By Sean Curran, Parliamentary Correspondent
The Parliamentary wrangle over the legal advice given to ministers about the Brexit deal is now coming to a head.
The Speaker’s decision to give the go-ahead for a contempt motion means that a debate over whether or not senior ministers flouted Parliamentary rules will now be the curtain raiser to five days of debate on Theresa May’s withdrawal agreement.
It also means that debate can’t start until the Commons has taken a decision on the contempt motion.
The vote on that motion could be an indication of what will happen in a week’s time, when the crunch vote on Brexit is due to take place.
Lib Dem Brexit spokesman Tom Brake, who campaigns for a further EU referendum, said: “Parliament is finally taking back control from this chaotic government.
“The attorney general put on a good show, but the House did not want TV drama. MPs expect the publication of the full legal Brexit advice before the debates on the withdrawal deal begin.
“The government must not be allowed to use this chaotic situation to take focus away from the mess they are making of Brexit.”
During a stormy debate in the Commons. Labour claimed Mr Cox was “hiding” his full legal advice “for fear of the political consequences”.
Mr Cox told MPs to “get real and grow up” – and his legal advice had no bearing on the political reality of the Brexit deal.
He conceded that the UK would be “indefinitely committed” to EU customs rules if Brexit trade talks broke down, under the terms of the withdrawal agreement hammered out in Brussels by Theresa May.
But he said it would not be in either side’s political interests to allow that to happen.
He described the controversial Northern Irish backstop as a “calculated risk”, adding that he did not think “we are likely to be entrapped in it permanently”, as some Brexiteers have claimed.
“We are indefinitely committed to it if it came into force. There is no point in my trying any more than the government trying to disguise that fact,” he told MPs.
He said he would have preferred to see a clause inserted into the EU withdrawal agreement that allowed the UK to exit the backstop if negotiations “had irretrievably broken down”.
But he added that he would back Mrs May’s deal because it was “a sensible compromise”.
What is the Northern Ireland backstop?
The Northern Ireland “backstop” is a last-resort plan designed to prevent a return to a visible border on the island of Ireland, with both the UK and the EU saying they want to avoid anything which puts the peace process at risk.
It would be triggered if no trade deal has been agreed with the EU that avoids the need for a hard border by the end of the 21-month transition period after 29 March’s official departure date.
It would keep the whole of the UK tied to EU customs rules, unless the two sides come up with another way of avoiding border checks.
Under the EU withdrawal agreement, neither side can unilaterally withdraw from it – but it is meant to be temporary.