Speaker John Bercow said ministers could face a debate on whether they are in contempt of parliament after it emerged important Brexit legal advice will remain secret.
MPs voted unanimously to force ministers to reveal the full legal advice on the Brexit deal after a debate in the Commons earlier this month.
Cabinet Office minister David Lidington promised the government would comply.
But on Wednesday, Prime Minister Theresa May faced accusations she was defying the will of the Commons by saying a “full, reasoned position statement” would be published instead.
The move sparked anger from MPs of all parties and Labour’s Keir Starmer has signalled he will seek a debate on whether the government holds parliament in contempt.
Shadow Brexit secretary Starmer told MPs he was “deeply concerned” that ministers intended to ignore the motion calling on them to publish the advice.
Starmer asked Bercow what he should do to ensure ministers published the advice “in full and in time to inform the meaningful vote” on May’s Brexit deal.
Bercow replied he was “free to write to me as early as he likes to suggest that the house has seen or is about to be subject to a contempt and seeking precedence for a motion to deal with it”.
He added: “It will be for me to decide, and I will not linger, whether there is an arguable case that a contempt has been committed and therefore whether an appropriate motion should be put urgently before the house.”
It is thought the legal advice, which has been presented to Attorney General Geoffrey Cox, includes alarming lines about the Northern Irish backstop customs arrangement.
The paper is expected to say that the joint UK-EU mechanism to end the arrangement amounted to an effective EU veto on when the UK can leave – something which would enrage Tory Brexiteers and the DUP.
DUP MP Nigel Dodds, whose party props up May’s government since the Tories lost their majority at the last election, underlined the point, suggesting the government could lose any vote put to MPs on the issue.
He said it was “felt widely across all parties” that the full legal advice was published, adding: “I really do hope that the motion that was passed will be delivered in full, because we made it very clear on the day of the debate where we stood and we expect the government to respond in full to the will of the house.”
Asked about the possibility of a contempt motion, the PM’s official spokesman said: “Our position is we are honouring the commitment we gave on the floor of the house.”