The parties have been mulling whether to agree to Johnson’s plan for a mid-October election, which can only be triggered if two-thirds of lawmakers agree.
Johnson already lost a vote on the same question this week, but plans to try again Monday, saying an election is the only way to break the country’s deadlock over Brexit.
Opponents don’t want to endorse the election unless they can ensure Johnson can’t take Britain out of the European Union as scheduled on Oct. 31 without a divorce agreement in place, as he has threatened to do so.
After discussions Friday, opposition lawmakers said they would not back an election until the government asked the EU to delay Brexit. Johnson said Thursday he would “rather be dead in a ditch” than do that.
The parties said they would either vote against Johnson’s motion or abstain on Monday.
Parliament is in the midst of passing an opposition-backed law that would compel the Conservative government to seek a Brexit postponement if no deal is agreed by late October. The bill is likely to become law by Monday, and many pro-EU lawmakers want to hold off on triggering an election until it is set in stone, fearing Johnson will try to wriggle out of the commitment.
“I do not trust the prime minister to do his duty,” said Liz Saville Roberts, the leader of the Welsh party Plaid Cymru.
She said lawmakers needed to be sitting in Parliament in late October, rather than on the campaign trail, to ensure Britain does not crash out of the EU.
Johnson said on Friday he was not willing to contemplate resigning.
"I'll go to Brussels, I'll get a deal and we'll make sure we come out on October 31 – that's what we've got to do," Johnson told Sky News during a visit to Scotland.
When asked if he would resign if he could not deliver that, he said: "That is not a hypothesis I'm willing to contemplate."
Johnson became prime minister in July after promising Conservatives that he would complete Brexit and break the impasse that has paralyzed Britain’s politics since voters decided in June 2016 to leave the bloc and which brought down his predecessor, Theresa May.
After only six weeks in office, however, his plans to lead the UK out of the EU are in crisis. The EU refuses to renegotiate the deal it struck with May, which has been rejected three times by Britain’s Parliament.
Johnson’s push to leave the EU by Halloween even if there is no divorce deal to smooth the way, is facing stiff opposition, both in Parliament and in the courts. Most economists say a no-deal Brexit would cause severe economic disruption and plunge the UK into recession.
On Friday, Britain’s High Court rejected a claim that Johnson is acting unlawfully in suspending Parliament for several weeks ahead of the country’s scheduled departure from the EU.
Johnson enraged his opponents by announcing he would send lawmakers home at some point next week until Oct. 14, just over two weeks before Britain is due to leave the EU. Critics accused him of subverting democracy and carrying out a “coup.”
A panel of three High Court judges ruled against her, but said the case can be appealed to the Supreme Court, which has set a hearing for Sept. 17.
AP and Reuters contributed to this story.