LONDON — The UK Supreme Court has ruled that Prime Minister Boris Johnson’s controversial decision to suspend parliament was unlawful.

The prime minister “prorogued” parliament for five weeks at the start of September, arguing the suspension would allow him to set out a new domestic agenda in a Queen’s speech.

But in announcing the verdict on Tuesday, the president of the Supreme Court, Lady Hale, said the prorogation was “void and of no effect,” adding: “Parliament has not been prorogued.”

Lady Hale announced that the court’s judgment was the unanimous judgment of all 11 justices, adding the case is a “one-off,” having come about “in circumstances which have never arisen before and are unlikely to ever arise again.”

She told the court that “a decision to prorogue, or advise the monarch to prorogue, will be unlawful if the prorogation has the effect of frustrating or preventing without reasonable justification the ability of Parliament to carry out its constitutional functions as a legislature and as the body responsible for the supervision of the executive.”

Reacting to the verdict, House of Commons Speaker John Bercow announced MPs will return to the House of Commons on Wednesday at 11:30 a.m.

Prime Minister Johnson was in New York for a UN summit on climate change when the ruling was announced ― which was at around 5:30 a.m. New York time.

“I have to say that I strongly disagree with what the justices have found,” he said. But he said that MPs will now come back to parliament.

Downing Street also reportedly dismissed calls for Johnson’s resignation.

Johnson is scheduled to meet with U.S. President Donald Trump at 11:15 a.m. local time.

After the verdict, opposition parties began calling for Johnson’s resignation. Labour leader Jeremy Corbyn, speaking at his party’s conference in Brighton, said Johnson should “consider his position” as prime minister.