Biden’s tailpipe emissions rules are at risk. Here’s why

That’s because the rules target mobile sources of greenhouse gas rather than stationary ones like power plants, even though environmental laws are ambiguous on whether regulators have the mandate to do that.

A U.S. Supreme Court decision limiting federal regulatory powers to interpret ambiguous laws could undermine President Joe Biden’s effort to cut tailpipe emissions from the nation’s vehicle fleet, two environmental law attorneys told Reuters.