New Delhi, Aug. 1 -- Appellate court judges expressed broad skepticism Thursday over President Donald Trump's legal rationale for his most expansive round of tariffs.

Members of the 11-judge panel of the U.S. Court of Appeals for the Federal Circuit in Washington appeared unconvinced by the Trump administration's insistence that the president could impose tariffs without congressional approval, and it hammered its invocation of the International Emergency Economic Powers Act to do so.

"IEEPA doesn't even mention the word 'tariffs' anywhere," Circuit Judge Jimmie Reyna said, in a sign of the panel's incredulity to a government attorney's arguments.

Brett Shumate, the attorney representing the Trump administration, acknowledged in the 99...