U.S. regulators threatened a ban of alcoholic energy drinks Wednesday in response to growing concerns over the safety of drinks like Four Loko, which has been linked to a number of deaths.

The Food and Drug Administration (FDA) sent official warning letters to the manufacturers of four caffeinated alcohol beverages Wednesday, and said it would not rule out seizing their products in the name of safety.

“FDA does not find support for the claim that the addition of caffeine to these alcoholic beverages is ‘generally recognized as safe,’ which is the legal standard,” principal deputy commissioner Dr. Joshua M. Sharfstein wrote. “To the contrary, there is evidence that the combinations of caffeine and alcohol in these products pose a public health concern.”

The companies, including the makers of popular malt beverages Four Loko and Joose, were given fifteen days to prove they would stop selling caffeinated products.

Phusion Projects, the maker of Four Loko, had already announced a day earlier that it would strip its fruity canned beverages of all caffeine.

“We have repeatedly contended -- and still believe, as do many people throughout the country -- that the combination of alcohol and caffeine is safe," Phusion co-founders Chris Hunter, Jeff Wright and Jaisen Freeman said in a statement. "If it were unsafe, popular drinks like rum and colas or Irish coffees that have been consumed safely and responsibly for years would face the same scrutiny that our products have recently faced."

Four Loko, which has been dubbed "blackout in a can" by some drinkers, sells for under $3 and contains as much alcohol as nearly five beers and as much caffeine as several cups of coffee.

Michael Michail, CEO of Joose parent company United Brands, said the company disagreed with the FDA actions, but did not address whether the drink's formula would be altered.

But the creator of one beverage flagged by the FDA told NewsCore she was "blindsided" by the decision, and criticized the agency for jumping to conclusions on the issue.

"Clearly this is a politically-charged event," said Rhonda Kallman, maker of Moonshot, a caffeinated beer threatened by the FDA letters. Sen. Charles Schumer (D-NY) and a string of state attorneys general had called for a complete ban in recent days.

"They just used a paintbrush and painted anything that has caffeine as evil," she said, pointing out that a number of spirits are still on the market with coffee content.

Moonshot, which is available in several major US cities including Atlanta and Los Angeles, has one-third of the alcohol proportion of Four Loko, and a fraction of the caffeine.

"Now there's no place for beer lovers to get a little pick-me-up," Kallman said.