Russian anti-war presidential candidate Boris Nadezhdin has that Russia's Central Election Commission working group had found 15% of the supporters' signatures he submitted to back his election bid to be invalid.
That figure, if confirmed, is three times higher than the allowable error rate and would provide grounds for the commission to disqualify Mr Nadezhdin from running against Vladimir Putin in March.
Mr Nadezhdin said on Telegram that he would appeal to the Supreme Court if the commission refused to register him.
"We plan to collect signatures. We only need to remove approximately 4,500 signatures out of 9,209 that were declared invalid," he said.
The commission will make a final ruling on the matter on Wednesday.
Mr Nadezhdin last week presented the electoral commission with signatures from more than 100,000 supporters across Russia as part of his bid to get his name on the ballot paper.
