Thirteen United and United Express planes were stuck on runways one day in July of last year. Thunderstorms disrupted air travel that day.
Under federal laws, after three hours, airlines must give passengers an opportunity to leave the plane. The transportation department says it's the biggest fine against an airline since those laws went into effect in 2010.
United said it is committed to complying with the tarmac delay regulations and we continue to improve its procedures.
