Tequila is for sipping, not shots - and certainly not for chugging out of a beer bottle with trace amounts of Mexico's most famous export. At least that's the stance of the country's Tequila Regulatory Council, which is threatening to sue Heineken over its tequila-flavored beer Desperados, the Financial Times reports.

Desperados' supposed link to tequila is pretty thin—it's made with some beer that's been aged in tequila barrels, plus beer that includes tequila and lemon "flavors."

The Tequila Regulatory Council, a trade group of Mexican tequila producers, says the beverage is in violation of designation of origin rules: it's using the name tequila but doesn't contain significant quantities of the spirit. But it's not hard to see how Desperados is offensive to tequila makers in other ways: The beer brand targeted at millennials goes against the sophisticated image tequila sellers have been trying to cultivate for years.

Promoters of Mexico's signature drink have been marketing it as a high-end spirit, and downplaying its former image as a quick way to get drunk at wild parties. Some shots of tequila now sell for more than $100, and last week actor George Clooney's tequila brand sold for $1 billion.

"We cannot permit someone unscrupulously to affect tequila's prestige," the Council's director general told the FT.

The group says tests show that Desperados does not contain tequila, and is giving Heineken until the end of the month to stop labeling its bottles with the word "tequila."

Heineken says that Desperados does contain bona fide tequila, but won't disclose exactly how much.

Tequila-flavored beer has met with a mixed reception among drinkers. Heineken discontinued Desperados in the United States in 2015 due to weak sales, and Anheuser-Busch canceled its own Oculto beer in 2016.