British Airways has apologized for delays caused by computer glitches in check-in systems — and warned that there may be further troubles.

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

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

BA had to apologize 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."