Officials said the company was also cited for underreporting incidents involving lost bags, overbooking and animals in transit, WMAQ-TV in Chicago reported. As a result, United made its performance look better on paper than it was in practice, a spokesman said.
United was spared a fine for the underreporting because the airline told the DOT about the problems and improved its procedures, officials said.
"When passengers are owed a refund, they have the right to expect the airline to act promptly and give them their money back," Transportation Secretary Anthony Foxx said in a release. "We also expect airlines to file accurate and timely consumer reports so that passengers will have the information they need when choosing an airline."
Under DOT rules, passengers who paid with credit cards are supposed to get refunds within a week, extended to 20 days for those who paid by cash or check.
Notable deaths of 2014 [PHOTOS]
GM recalls 221,000 Cadillacs and Impalas