The opposition Congress for Democratic Change said it wanted a new election commission to make sure ballots in next week's vote wouldn't be compromised, Voice of America reports.
Former diplomat Winston Tubman, who ran for president on the CDC ticket, said, however, he'd take part in the contest after election Chairman James Fromayan resigned.
The Liberian election commission was upended after a series of allegations surfaced that it was quietly backing incumbent President Ellen Johnson Sirleaf.
The incumbent won the most votes in last month's election but not by enough to secure an outright victory.
The Liberian National Election Commission said it was investigating 16 of the 54 complaints filed in connection with the October vote.
Acting NEC Chairwoman Elizabeth Nelson said in a statement that "all necessary measures" were in place for the Nov. 8 runoff.
Sixteen candidates took part in the Oct. 11 contest. Sirleaf won 43.9 percent of the vote and Tubman secured 32.7 percent of the estimated 1.3 million votes cast.
Fourth-place candidate Charles Brumskine, who's Liberty Party took 5.5 percent of the vote, has endorsed Sirleaf in the second round.