As e-cigarettes have flooded the market, the FDA's role in approving new tobacco products is put under a microscope.

The high court is taking up an appeal from the Food and Drug Administration, which has denied more than a million applications to sell candy- or fruit-flavored products that appeal to kids.

The Supreme Court on Monday pressed the Food and Drug Administration on whether it followed the law in its effort to keep flavored e-cigarettes off shelves, weighing a lawsuit from a multibillion-dollar industry that has come under scrutiny because its products are popular with school-aged children.