The court urged the commission to hear the Liberty Party's complaint and resolve it with "urgent attention", given the "critical" nature of the presidential vote.
The Supreme Court of Liberia on Monday halted a presidential runoff election scheduled for Tuesday, delaying the first democratic transfer of power in the West African country in recent political history.
The decision throws Liberia's first democratic transition in seven decades into uncertainty a day ahead of what was to have been the final round of voting to pick between former global footballer George Weah and incumbent vice-president Joseph Boakai.
The court on Monday announced the decision, saying the election would not go ahead until a legal complaint alleging voter fraud and irregularities by the opposition Liberty Party is resolved.
The poll can not be held until the electorn commission "urgently and expeditiously" investigates allegations of "irregularities and fraud" made by the opposition Liberty Party, the court said.
Liberia is no stranger to disputed election results: Weah's CDC party challenged but ultimately accepted the results of presidential votes in 2005 and 2011.
Boakai's Unity Party signed a letter accusing the president of "interference" by meeting polling officials at her home before the election, and he maintains "there is a reason to raise qualms" if the meeting was indeed at her residence.
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With Atletico Madrid in third place and yet to win in the Champions League this season, it could be a major scalp for both sides. Fabregas came off midway through the second half with Danny Drinkwater getting his Champions League debut.
A hint of Boakai's true motive in supporting the fraud allegations, critics say, was clear in a leaked early draft of a speech given on October 23.
Her spokesman has said the meeting was in the course of the normal actions of a concerned president.
"Individuals close to her and operating under her instructions are in fact giving multiple forms of support to our main opponent in the presidential race, the Coalition for Democratic Change (CDC)", according to the draft, which was seen by AFP, before more diplomatic wording was added at the last minute.
Its candidate, Charles Brumskine, was eliminated from the run-off after he came third in last month's election.
Commentators describe the election - showcased as Liberia's first democratic transition in seven decades - as a key test of stability after Sirleaf's presidency, which followed back-to-back civil wars between 1989-2003 in which an estimated quarter of a million people died.
"We do not want no violence".
National Elections Commission lawyer Musa Dean told The Associated Press "the highest court of the land has spoken and we have to abide by the ruling".