Millions of litres of Italian wine may have been blended illegally, in a fresh fraud investigation that threatens to further damage Italy's standing on the world wine market.

Italian authorities are investigating whether large quantities of quality wine from the Tuscany region have been illegally bulked up with lower end wine and with grape varieties forbidden by local production rules.

Up to 10m litres of wine may be affected, according to Italian press reports at the weekend.

Tuscany-based Chianti Classico is not involved in the investigation, a spokesperson for the denomination told just-drinks today (15 December).

However, she said that producers of high-end Chianti DOCG wines and Toscana IGT are involved. Press reports have also cited Brunello di Montalcino, which was subject to a similar investigation over its 2003 vintage.

A fresh scandal in Italian wine threatens to cast further doubt on Italy's ability to guarantee the quality of wine and accuracy of bottle labels.

"I believe this new wine scandal confirms the existence of a real system, including well-known and celebrated wineries and their winemakers, that do not respect the wine laws," Italian wine expert Franco Ziliani told just-drinks.

Some producers have acted "arrogantly" by flouting production rules in their region, said Ziliani, who also runs the wine blog vinoalvino.org.

"Finally the authorities decided to see what was happening and the results are the wine scandals that periodically explode in my country," he said.

No charges have yet been brought in the latest investigation in Tuscany.

Back in 2008, some of the biggest names in one of Italy's most famous wine regions - Brunello di Montalcino - had their 2003 vintage stocks impounded by police pending a fraud investigation.

The scandal led to a threat from the US that it would block imports of the wine.

Stocks were subsquently released later in the year, but authorities accused 17 people of wrongdoing in a report published in summer 2009. It has remained unclear whether charges will be brought.