DALLAS (AP) — Southwest Airlines scrubbed thousands of flights again Tuesday in the aftermath of the massive winter storm that wrecked Christmas travel plans across the U.S., and the federal government said it would investigate why the company lagged so far behind other carriers.

A day after most U.S. airlines had recovered from the storm, Southwest called off about 2,600 more flights on the East Coast by late afternoon. Those flights accounted for more than 80% of the 3,000 trips that got canceled nationwide Tuesday, according to tracking service FlightAware.

And the chaos seemed certain to c...