"There has been a notice of a violation," a spokesman said but could not confirm newspaper reports that the positive was the result of a re-test of a January sample, taken after Schwazer had qualified for the Rio De Janeiro Olympics.
Schwazer, who won the European 20km title in 2010, served a ban of three years and nine months after admitting using the EPO blood-booster in 2012, and now faces a life ban from the sport.
Italian media quoted his lawyer Gerhard Brandstatter saying: "These are false and monstrous accusations.
"What Alex has always feared has happened, but we will defend ourselves and we will sue," he said.
He added that he did not understand why a sample tested negative for banned substances in January and a second test on the same sample in May showed up positive.
An assistant to Brandstatter declined to comment and would not confirm Brandstatter's comments reported by Italian newspapers including La Repubblica and La Gazzetta dello Sport.
Before Schwazer's 2012 ban and exclusion from the 2012 London Games, he was a hero in Italy after winning Olympic gold, beating a 20-year-old record set by Russian Vyacheslav Ivanenko by more than a minute.
An assistant to one of the athlete's coaches said Schwazer would hold a news conference later on Wednesday.
(Reporting by Isla Binnie and Steve Scherer, editing by Mitch Phillips and Ken Ferris)
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