LONDON (AP) — British Airways travelers are suffering delays globally due to computer glitches in the check-in systems, with the company warning that there may be further trouble.

Travelers took to social media to complain of long lines and the airline said "a number" of airports were affected.

The airline apologized and said passengers are being checked in at Heathrow and Gatwick Airports but that the process may be "a bit slower than usual."

BA had to apologize already in July after computer glitches in check-in systems also delayed passengers. It began installing new systems last October and completed the rollout earlier this year.

BA says it would "encourage customers to check in online before they reach the airport."

The airline's problems come barely a month after U.S. carrier Delta Air Lines Inc. suffered a global outage that caused it to cancel 2,300 flights.