Romania’s Constitutional Court has ordered a recount of votes annulled in last Sunday’s presidential run-off vote.
It follows claims of widespread fraud by the opposition Social Democrats.
Around 138,000 ballots will be re-examined, raising the prospect of Traian Basescu’s narrow victory being overturned.
The incumbent leader won with a 70,000 vote margin, but some analysts say it is unlikely enough annulled votes will be declared valid to make a difference.
Speaking in Brussels, Basescu dismissed the challenge to the result as part of a normal democratic process.
Both party leaders declared themselves winners after last Sunday’s vote.
But Social Democrat candidate Mircea Geoana still harbours hopes of a rerun as the court must rule on another complaint.
His party also allege there was massive multiple voting and vote buying.