The U.S. Supreme Court grappled on Monday with the U.S. Food and Drug Administration's defense of the agency's refusal to let two e-cigarette companies sell nicotine-containing flavored vape products that regulators found to pose a significant health risk to youths.

The focal point of the case is 2009 law enacted by Congress that gives the Food and Drug Administration a mandate to curb the availability of nicotine products for minors.