Spokesperson for Ruffino, Lene Petersen, said police had sealed off its entire stock of Chianti Classico wine, about 70,000 hectolitres, in its cellars.
The move comes as part of a fraud inquiry into wine supplier Piero Conticelli, who stands accused of selling wine made from grapes that have been grown in vineyards not registered as Chianto Classico DOCG (strictly controlled origin and quality).
Ruffino, now partly owned by wine giant Constellation Brands, was the biggest customer for Conticelli's Cavico company, buying his wine to use in producing its own in-house Chianti Classico. Other wine estates supplied by Conticelli are also thought to be involved.
Petersen said Ruffino's stock had been "preventatively frozen until the police can pin-point exactly which wines are actually involved. We don't know if it has gone to Ruffino or someone else."
The root of the allegations against Conticelli are based on anomalies uncovered in Cavico's accounts.
But, the fresh police action risks striking a blow to the reputation of Italy's most prestigious wine classification, something all producers will be wary of at a time of fierce competition in the world wine market.
Italy is currently the world's biggest wine exporter with a 21 per cent of the market, closely followed by France and Spain on 19 per cent. Yet a global over-production problem and the continuous rise of New World varieties has put greater pressure on the European 'big three'.
Constellation brands has also spent much of 2005 relying on its stake in Ruffino for an increase in sales. Ruffino and the newly acquired Robert Mondavi helped Constellation's branded wines to a 59 per cent sales increase in its second quarter.
Petersen said that no suspicious Chianti Classico wine from Ruffino was thought to be on the market, yet the biggest problem for the group is how long it can continue to supply markets with more than nine million bottles' worth of wine locked up.
"We don't know how long this will last for yet, we are hoping we will get some news next week," said Petersen, adding that the firm was "at risk of running out of stock".
She said this was a very real danger in countries that require firms to maintain a certain level of stock, such as Canada and those in Scandinavia.
At the moment the group is coping. "We always keep a fairly good stock in those markets because you always have to be prepared. Right now we are working togther with the authorities."