By their reading, the emergency powers act permits the president to wield tariffs as a bargaining chip, and government lawyers told the court that it owed “substantial deference” to Mr. Trump on how to respond to a national emergency. The White House did not respond to a request for comment for this article.

U.S. President Donald Trump gave Mexico a 90-day reprieve from higher tariffs to negotiate a broader trade deal but was expected to issue higher final duty rates for most other countries as the clock wound down on his Friday deal deadline.