Theresa May has been accused of running a government "in chaos" as it refuses to confirm whether the Queen's Speech will have to be delayed.
The Queen is due to set out the Government's programme on 19 June, but the key address may be postponed as the Prime Minister continues talks with the Democratic Unionist Party to secure their support in propping up her minority government.
With her authority diminished after failing to secure a majority in the election, Mrs May faces the prospect of relying on the DUP to make sure the Queen's Speech passes.
She is meeting with the party's leader Arlene Foster on Tuesday to finalise a deal.
Mrs May's most senior minister, First Secretary of State Damien Green, said: "Obviously until we have that we can't agree the final details of the Queen's Speech."
He could not say when the Queen would now open Parliament, adding: "I can't confirm anything yet until we know the final details of the agreement.
"We know those talks are going well and also we know that, at this very important time, we want to produce a substantial Queen's Speech."
On Monday afternoon, the Prime Minister faced a showdown with backbench MPs on the influential 1922 Committee.
She was greeted to the meeting with around 25 seconds of table-banging and a brief cheer - far from the acclamation she might have expected if she had returned from the election campaign with a healthy majority.
During the meeting, she told MPs: "I'm the person who got us into this mess, and I'm the one who will get us out of it."
The committee's chairman has said he does not see any "clamour" for a leadership contest.
Opposition parties wasted no time in criticising Mrs May over the potential delay to the Queen's Speech.
A Labour spokesperson said: "Number 10's failure to confirm the date of the Queen's Speech shows that this government is in chaos, as it struggles to agree a backroom deal with a party with abhorrent views on LGBT and women's rights."
Liberal Democrat leader Tim Farron said: "This is an utter humiliation for Theresa May. It is time to stop trying to cling to power and time to admit enough is enough."
Additional delay could be caused because the Queen's Speech is written on goatskin parchment paper, which requires several days for the ink to dry.
The paper does not contain any goatskin, but is high-quality archival paper that is guaranteed to last for at least 500 years.
Earlier, Brexit Secretary David Davis signalled that official negotiations with the EU may not start on 19 June as anticipated.
He said talks would start next week, but not necessarily on Monday.
He told Sky News: "It's in the week of next week, basically, the first discussions. My permanent secretary is actually in Brussels today talking to them about the details."
Mr Davis also suggested Mrs May could have to rethink her approach to Brexit after losing seats in the snap election.
He added that some manifesto pledges would be dropped or watered down as he admitted the Tory election campaign "went wrong".
"We'll have to look at the Queen's Speech and what we have to get through," he said.