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 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.
Labour foreign affairs spokeswoman Emily Thornberry said Johnson was "as slippery as can be" and could not be trusted.
Johnson's push to leave the EU by Halloween, with or without a divorce deal to smooth the way, is facing stiff opposition, both in Parliament and in the courts.
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."
Transparency campaigner Gina Miller took the government to court, arguing the suspension was an "unlawful abuse of power."
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.
Outside court, Miller said she was disappointed with the ruling but "pleased that the judges have given us permission to appeal to the Supreme Court."
"To give up now would be a dereliction of our responsibility," she said. "We need to protect our institutions. It is not right that they should be shut down or bullied, especially at this momentous time in our history."
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