ROME—Some things should be sacred. And for many Italians wine is high on that list along with the belief that what is stated on a label is what’s actually contained in a bottle.

But a sting operation carried out this week across a dozen Italian wine-producing regions has exposed a rather sour practice. At least 50 entities tied to wine production, including vineyards and bottling companies, according to Italy’s health protection agency, are under investigation for cutting expensive wines with mediocre grapes.

The suspected fraudulent wines are fortunately not dangerous to drink—nor are they necessarily even bad tasting—but they aren't worth what they are being sold for. Better Italian wines have coveted classifications like DOP, IGP and DOC, which guarantee their authenticity and adherence to specific methods and practices. These special categories also provide assurance that the grapes come from certain regions.

Those classifications are literally badges of honor and are only granted through tedious inspections and compliance to regulations that can be costly to wine producers, which then justifies higher retail prices.

The companies under investigation include prestigious wines from Pordenone, Udine, Treviso, Venice, Padova, Reggio Emilia, Modena, Ravenna, Florence, Livorno, Naples and several cities in Puglia. The prosecution has not released a full list of brands involved, but is expected to do so in the coming days as search warrants are served and further inspections are carried out.

But it is clear that not only producers are involved. Inspectors that doled out classifications for these imposter wines are also under investigation for complicity.

“The investigations are aimed at acquiring evidence related to fraudulent behavior,” said the local prosecutor in Pordenone in northern Italy, where the discoveries were first made. “The problem is with the production and placing huge quantities of wine on the market that, despite not constituting a danger to the health of the consumer, have been produced in direct violation of the rules of the specifications granted.”

The prosecutor leading the case believes that extreme weather conditions in recent years likely contributed to both an overproduction of grapes in less important wine regions and a shortage of grapes in more sought-after wine regions. In order to keep up with the demand for the more expensive bottlings, some brands are suspected of breaking the law and using cheaper grapes from other parts of the country. The small amount of wine actually made in the better regions was likely kept in Italy and the imposter wine was mostly exported.

Officials investigating the case have opened a parallel anti-mafia investigation to determine if any of Italy’s organized crime syndicates who specialize in so-called agro-mafia practices are involved.

Italy’s national agricultural association Coldiretti says agro-mafia practices have infiltrated many of the country’s most famous made-in-Italy exports. “The turnover of the agro-mafia exceeds $18 billion a year,” says Coldiretti chief Domenico Pautasso, adding that “the entire system of false made-in- Italy products exceeds $68 billion a year.”

In 2015, several major olive oil producers were charged with cutting extra- virgin olive oil with imported canola and soybean oil in a scandal that led straight to Italy’s organized crime syndicates who had found a way to siphon money off the scam. The olive oil fraud led to the discovery of more than 350,000 farmers and producers who were either directly complicit or who unknowingly sold their products to companies who were involved in fraudulent behavior in labeling and exporting practices.

In 2014, the Italian wine industry was rocked by a similar scandal to what is currently unfolding. Then, more than 30,000 bottles of wildly expensive Brunello, Chianti Classico and Sagrantino di Montefalco were taken off store shelves and pulled out of restaurants after it was discovered that they were cut with grapes that made them nearly worthless.

This new investigation is expected to take weeks in order to assess the full scale of the fraud but, no doubt, it will leave many drinkers around the world with a bad taste in their mouth.