WASHINGTON (Reuters) -The U.S. Supreme Court threw out on Wednesday a judicial decision that found the U.S. Food and Drug Administration acted unlawfully in refusing to let two e-cigarette companies sell flavored vape products that regulators consider a health risk to youths.

The justices in a unanimous ruling threw out a lower court's ruling that the FDA had failed to follow proper legal procedures under a federal law called the Administrative Procedure Act when it rejected the applications by the companies, Triton Distribution and Vapetasia, to sell these nicotine-containing products.

An FDA rule that took effect in 2016 under Democratic President Barack Obama deemed e-cigarettes to be tobacco products that, like traditional cigarettes, are subject to agency review under a 2009 federal law called the Tobacco Control Act. The law requires manufacturers of e-cigarette products to apply for authorization to sell nicotine vaping devices and e-liquids.

Triton Distribution and Vapetasia filed FDA applications in 2020 for products with flavors such as sour grape, pink lemonade and crème brulee, and names including "Jimmy The Juice Man Peachy Strawberry" and "Suicide Bunny Mother's Milk and Cookies" - offerings that critics have said were designed to appeal to minors. The FDA denied the Triton and Vapetasia applications as well as hundreds of others by various companies involving more than a million flavored vape products.

During arguments in the case, a Justice Department lawyer arguing for the FDA said the companies knew throughout the application process that the agency was concerned about the fact that flavors are attractive to youth and about the addictive nature of nicotine, a chemical dangerous to developing brains.

In order to win regulatory approval, e-cigarette companies must demonstrate that a product would be "appropriate for the protection of the public health." That means that any health benefits - such as helping traditional cigarette smokers transition to generally less-harmful vaping - must outweigh the risks of bringing the new product to market.

The e-cigarette companies argued that the FDA improperly assessed their applications under a regulatory standard that differed from published guidance they had relied upon.

The FDA found that in 2020 nearly one in five high school students and almost one in 20 middle school students used e-cigarettes, making e-cigarettes "the most widely used tobacco product among youth by far."

The agency over the years has approved only 34 flavored e-cigarette varieties, all tobacco or menthol flavored. It maintains that it has not categorically banned flavored e-cigarette products. But companies seeking its approval to sell these products face an especially tough health benefits-versus-risk legal test as a result of the FDA's finding that flavored e-cigarettes pose a "known and substantial risk" to youth.

Triton and Vapetasia in 2021 asked the New Orleans-based 5th U.S. Circuit Court of Appeals to review the FDA's denial of their applications. The full slate of 5th Circuit judges ruled 10-6 that the FDA had been arbitrary and capricious, in violation of a federal law called the Administrative Procedure Act, by denying the applications without considering plans by the companies to prevent underage access and use.

Seven other federal appellate courts had sided with the FDA in similar cases.

The Supreme Court on Nov. 25 also declined to hear an appeal by RJ Reynolds and other tobacco companies of a lower court's ruling upholding graphic health warnings required by the FDA on cigarette packs.

The Supreme Court, with a 6-3 conservative majority, has reined in the authority of federal agencies in a series of cases in recent years. In another high-profile case involving the FDA, the Supreme Court in June decided on procedural grounds to reject a bid by anti-abortion groups and doctors to restrict access to the abortion pill mifepristone.