Inter Beaujolais, the organisation representing wine producers in Beaujolais, has threatened to sue any winemakers found guilty of illegally enriching their wines with sugar.

Between 100 and 150 winemakers may be questioned by French police over whether they added more than the legal amount of sugar to their wines, a source told France's Le Monde newspaper.

News of a fresh scandal comes as the region is attempting to lose an image of valuing quantity over quality.

Inter Beaujolais said it was taking the investigation seriously. "We strongly condemn illegal practices and would consider, if the inquiry shows they exist, starting legal action."

Police have been tracking a consignment of 600 tonnes of sugar they believe entered the Beaujolais area between 2004 and 2006.

The sugar disappeared, and suspicions have fallen on the area's 3,000 wineries. Enriching wines with sugar, predominantly to raise alcohol content, is allowed at 17g per litre.

But it is now thought some producers may have used the black market stock to add more than rules allow.

A source close to the inquiry told Le Monde: "These [winemakers] are evidently not criminals, but it appears they have benefited from this. They cannot escape the crime of drinks fraud."

The investigation comes only a year after producer Georges Duboeuf was fined for adding substandard wine to higher quality stocks.