Stam is the latest player to test positive for nandrolone
The league's disciplinary committee confirmed that the Lazio defender would be suspended from all sporting activity with immediate effect.
But no decision on a ban will be made until the result of a second test on the former Manchester United centre-half is known.
The decision follows an announcement by the Italian Olympic Committee (CONI) on Friday that Stam had tested positive for the banned steroid nandrolone after the Serie A game against Atalanta on 13 October.
"One thing I can say, without hesitation or doubt, is that I have never knowingly taken nandrolone or any other illegal substance.
"I am not - and never have been - a cheat and would never do anything like this to jeopardise the happiness of my family or the future of my career."
The Italian Olympic Committee (CONI) released a statement on Friday, detailing the circumstances in which the Dutch international failed his test.
"The Rome laboratory has revealed in the analysis a presence of the metabolic substance nandrolone," said the statement.
"The athlete has been found positive in the first analysis and will be immediately suspended from all sporting activities."
Stam, 29, who joined Lazio from United for £16.5m in August, is the second player at the Serie A club to fail such a test.
Portuguese international Fernando Couto has just returned from a ban, while Dutch team-mates Edgar Davids and Frank de Boer have also been suspended for use of the drug.
Juventus midfield man Davids was banned for five months and fined £32,000, but has since returned to action.
Lazio have rallied behind Stam, with the club's doctor insisting all possible steps have been taken to ensure players use only permitted supplements.
"We are all in shock at this news," said Dr Andrea Campi.