By Francois Murphy and Shadia Nasralla
VIENNA (Reuters) - Austria's far-right Freedom Party (FPO) on Wednesday formally contested the result of last month's presidential election, calling into question the count of postal ballots that swung the vote against its candidate.
Postal ballots pushed former Greens leader Alexander Van der Bellen past the FPO's Norbert Hofer in a tight run-off vote in which the margin of victory was less than 1 percentage point, or roughly 31,000 votes.
While the post of president is largely ceremonial in Austria, Hofer would have been the first far-right head of state in the European Union. Governments across the continent breathed a sigh of relief at his defeat.
FPO leader Heinz-Christian Strache called for a re-run of the election, saying his party had evidence of numerous irregularities, including the early counting of postal ballots - an issue many see as a technicality, not a serious breach.
"We are not bad losers. Rather it is about the foundations of democracy, which must be secured," Strache told a news conference announcing the challenge.
Various irregularities have already come to light, mostly involving the early counting and processing of postal ballots, but the interior ministry has said the number of votes affected was smaller than the margin of victory.
Strache said that figure was much higher.
"The scale of this observation is more than frightening and more than relevant. For this reason I feel obliged to challenge this result."
Austria's Constitutional Court must now determine whether the law has been broken and whether the breach might have affected the outcome of the election. It said it aimed to reach a verdict before Van der Bellen is due to take office on July 8.
The FPO challenge focuses on 573,275 of the more than 700,000 postal ballots cast in the election. Irregularities cited by the FPO included ballots being counted by unauthorized people or without observers present.
The Freedom Party's move threatens to revive a contest that split the country almost evenly in two, with workers and rural areas largely backing Hofer and cities and the highly educated leaning toward Van der Bellen.
The Interior Ministry has said that the overwhelming majority of votes judged irregular in the run-off were labeled thus because they were postal ballots processed or counted before 9 a.m. on the day after the election.
Up to 23,000 votes were affected, with a further 2,000 ruled out due to more serious violations such as when a handful of teenagers not yet of voting age were allowed to cast ballots, the ministry said.
(Additional reporting by Alexandra Schwarz-Goerlich; Editing by Gareth Jones)