Up to one-third of wines marketed under France's regional "appellation" system do not deserve the label, a leading French consumer group says.
Wine professionals surveyed by the UFC-Que Choisir group say controls have become more lax and have led to a collapse in quality.
Almost all wines presented for approval in 2004 and 2005 succeeded in winning the appellation (AOC) label, it says.
The group called for a reform of the system to reflect the grapes used.
"For a number of years, we've seen a steady fall in quality in a number of AOCs (appellation d'origine controlee), which has completely undermined consumer confidence," said Alain Bazot, the head of UFC-Que Choisir.
One in three AOC bottles were either of poor quality or did not demonstrate sufficient links to the region of origin, the study said.
Loose controls meant 98% all wines presented in 2004 were awarded their AOC label and 99% in 2005, it said.
In 30 years, AOC production has increased from 15 million hectolitres to 25 million.
In the 1970s, table wines accounted for 70% of French wine production and AOC wines for just 22%.
But table wine now account for just one-quarter of production, while 44% is AOC wines.
The study also questions the impartiality of the AOC panels, which are made up of local wine professionals described as "judge and jury" of their own produce.
UFC-Que Choisir is now calling for the national appellation institute, Inao, to take urgent steps to correct the situation.
It wants the system to be divided into genuine local appellations and more generic wines, based on grape varieties, to appeal to "modern" tastes and compete with wines from the New World.
The AOC certification system guarantees that some wines, cheeses and other agricultural products come from a particular region and meet quality standards.
When it comes to wine, the system specifies which grapes can be used, where they can be grown as well as permitted alcohol and sugar levels.
It is designed to give legal protection to wine-growing regions such as Bordeaux and Burgundy, and is supposed to act as a guarantee of quality, particularly for wines under the most prestigious AOC label.