Federal agencies moved aggressively Wednesday to eliminate from the market the potent alcoholic "energy" drinks spiked with caffeine that have become wildly popular on college campuses in recent years.

In letters to four companies, the Food and Drug Administration said it had concluded that adding caffeine to alcohol created "adulterated" products that were unsafe and illegal. If the companies do not take action within 15 days, the FDA could begin seizing the products or seek a court order barring companies from continuing to sell the products.

Simultaneously, Treasury Department officials announced that, based on the FDA's conclusion, the companies would be told that the products had been mislabeled and were, therefore, illegal to be shipped. And the Federal Trade Commission informed the same four firms that marketing their seven products risked violating federal law.

The drinks, sometimes called a "blackout in a can," contain high levels of alcohol and caffeine. The mixture creates a state of "wide-awake drunk" that makes it difficult for people to realize how intoxicated they are and enables them to consume far more alcohol than they otherwise would without passing out, officials said. That puts them at increased risk for alcohol poisoning, engaging in risky behavior such as driving drunk, and committing or being the victims of sexual assaults, they said. Consuming one can of Four Loko - the most popular product - has been compared to drinking five cans of beer and a cup of coffee.

Federal officials were facing increasing pressure to take action against the drinks in the wake of a series of high-profile incidents. Dozens of students at Central Washington University and Ramapo College in New Jersey, for example, recently were rushed to emergency rooms after consuming Four Loko, including some with alcohol poisoning and at least one near death. In other incidents, deaths and fatal car crashes have been blamed on the drinks.

"I call them killer cocktails," said Utah Attorney General Mark Shurtleff, who was among 18 attorneys general who had been pressing the FDA to take action for more than a year. "Young people have been dying after drinking this stuff. It's about time we're finally doing something about these dangerous drinks."

With the number of state bans increasing and the federal crackdown imminent, Phusion Projects of Chicago, which makes Four Loko and was one of the companies warned, announced Tuesday night that it was removing caffeine and other substances from all of its products. Federal officials said they were pleased by the announcement and would monitor the company to make sure it followed through quickly.

United Brands Co. of San Diego, which makes JOOSE, said the company disagreed with the FDA's "action and rationale, as well as the characterization of our products," had "seen no known reports of any health or safety incidents" involving its products and "will continue to produce quality products that meet the demands of our loyal adult consumers." However, the company said it would "continue engagement with alcohol regulatory bodies and legislators to ensure compliance with the latest guidance."

Charge Beverages Corp. of Portland, Ore., said it had already decided to discontinue making caffeinated drinks. New Century Brewing Co. of Boston did not respond to a request for comment.

While the move was praised by public health authorities, law enforcement officials and others, some criticized it as the latest example of the federal government being overly paternalistic, increasingly creating an intrusive "nanny state."

"The same legal argument could be used to ban everything from Mountain Dew and Dr Pepper to an array of popular candies and snacks that currently contain added caffeine," said Gregory Conko of the Competitive Enterprise Institute. "It's time the FDA started treating consumers old enough to purchase alcoholic beverages as adults."

Keiran Bleich, a junior at American University majoring in political science, voiced similar outrage.