Narungga MP-elect Chantelle Thomas claimed the Yorke Peninsula seat in South Australia by a margin of just 58 votes.
It gave One Nation four seats following the March 21 state election in a stunning result for the far-right party.
But after more than 80 uncounted ballot papers were uncovered for the seat, Ms Thomas is facing a recount and the prospect of her narrow victory being annulled.
"This raises serious questions about the integrity of the South Australian election," she said on Thursday.
Ms Thomas raised doubts about the commission's preparedness and SA's new electoral laws.Â
"This is very disappointing for my community in Narungga," she said.
"We're being forced to wait, again, to see who will be Narungga's representative in parliament."
The Electoral Commission of South Australia said a recount would be run on Friday "to ensure the integrity of the Narungga result".
"The purpose of the count is for the commission to determine whether the result would have differed had those ballots been included in the initial count and the subsequent recount," Deputy Electoral Commissioner Leah McLay said.
The commission is expected to seek legal advice and petition the Court of Disputed Returns if the new count changes the election result.
The uncounted ballots were in three sealed boxes and returned to the electoral commission, Ms McLay said.
"We have not investigated what the cause of the error was," she said.
Ms McLay said the SA electoral commission would support any independent external review into the 2026 state election.
Ms Thomas was declared the winner of Narungga earlier in April over the Liberal Party's Tania Stock following a recount due to the tight voting margin.
