VIENNA (Reuters) - Austria's Constitutional Court will rule on Friday on the far-right Freedom Party's challenge to the result of last month's presidential run-off election, which its candidate narrowly lost, a court spokesman said.

Postal ballots swung the election against Freedom Party candidate Norbert Hofer, who would have been the first far-right head of state in the European Union. He lost to former Greens leader Alexander Van der Bellen by less than a percentage point.

Witnesses have told the court of several cases in which postal ballots were counted sooner than they should have been - before 9 a.m. the day after the May 22 election, as officials tried to ensure the count was completed by Monday afternoon.

That and other signs of widespread sloppiness by election officials and political parties' observers have dismayed the public. They range from not attending the count to not reading forms they signed certifying the count was carried out properly.

It is unclear whether that will be enough for the court to find the law was broken in a way that could have influenced the vote's outcome - the standard for the challenge to succeed. The court can order remedies ranging up to a re-run of the election.

"The (Constitutional Court) will make its decision on (the presidential election) known on Friday July 1," court spokesman Christian Neuwirth said on Twitter on Thursday. "It will be announced publicly."

(Reporting by Francois Murphy; Editing by Hugh Lawson)