LONDON (Reuters) - British Supreme Court ruled on Tuesday that Prime Minister Boris Johnson's suspension of parliament was illegal, prompting opposition Labor Party leader Jeremy Corbin to demand Johnson resign and call early elections.

After three days of hearings and arguments against the parliament's suspension, Supreme Court President Brenda Hill said Johnson's decision to disrupt the parliament "was illegal, because it had the effect of frustrating the work of Parliament or preventing it from carrying out its legislative functions without reasonable justification."

"Parliament is not constrained. This is a unanimous decision by all 11 judges," Hill said. "The parliament - especially its speaker as well as the speaker of the House of Lords - has to decide what to do next."

House Speaker John Birko, who strongly criticized Johnson's decision, said parliament should "meet without delay" and said he would consult "without delay" with party leaders.

The prime minister announced that it was studying the ruling, while opposition leader Corbin seized the opportunity and said the ruling showed Johnson's contempt for democracy and a violation of power.

"I call on Boris Johnson ... to think about his position and become the prime minister for the shortest time ever," Corbin told a Labor conference, calling on the Conservative leader to "organize elections to choose a government that respects democracy."

Parliament's work was suspended between 10 September and 14 October, and Queen Elizabeth endorsed the decision on the advice of the Prime Minister as required by the Constitution.

A Scottish court had previously ruled that the six-week suspension of parliament was illegal, believing Johnson had taken the move to prevent parliament from scrutinizing his Brexit plans.