Complaints to US government from travellers are the highest since the COVID pandemic when airlines were slow to refund.

The Department of Transportation said Friday that it received nearly 97,000 complaints in 2023, up from about 86,000 the year before. The department said there were so many complaints that it took until July to sort through the filings and compile the figures.

That’s the highest number of consumer complaints about airlines since 2020, when airlines were slow to give customers refunds after the coronavirus pandemic shut down air travel.

The increase in complaints came even as airlines cancelled far fewer US flights — 116,700, or 1.2 percent of the total, last year, compared with about 210,500, or 2.3 percent, in 2022, according to FlightAware data. However, delays remained stubbornly high last year, at about 21 percent of all flights.

More than two-thirds of all complaints last year dealt with US airlines, but a quarter covered foreign airlines. Most of the rest were about travel agents and tour operators.

Complaints about treating passengers with disabilities rose by more than one-fourth compared with 2022. Complaints of discrimination, while small in number, also rose sharply. Most were about race or national origin.

Airlines receive many more complaints from travellers who do not know how or do not bother to complain to the government, but the carriers do not release those numbers.

The Transportation Department is modernising its complaint-taking system, which the agency says will help it do a better job overseeing the airline industry. However, the department currently releases complaint numbers many months late. It did not issue figures for the second half of 2023 until Friday.