A Virgin Atlantic employee has resigned amid allegations she passed on the flight details of eight celebrities to a paparazzi agency.
The airline is looking into claims the woman handed the information to the London-based agency and said it would "deeply regret" any concern caused to the passengers involved.
A Virgin Atlantic spokeswoman said: "The allegations that have been raised are extremely serious and we have launched an immediate investigation. The security of customer information is our highest priority and we have robust processes in place to ensure that passenger information is protected.
"The incident that has been alleged concerns eight customers' flights booked in 2010 and we are in contact with all of those people. It is too early to draw conclusions on this matter but of course we would deeply regret any concern that these allegations may cause the individuals involved."
The stars whose flight details were allegedly handed to Big Pictures agency are understood to be Chelsea footballer Ashley Cole, his former wife and singer Cheryl Cole, actress Sienna Miller, Tottenham footballer Jermain Defoe, actors Scarlett Johansson and Gwyneth Paltrow, and singers Robbie Williams and Nicole Scherzinger.
Virgin Atlantic has been attempting to contact them and a source at the company said it was scanning through email archives and investigating who could access its booking system.
The accused employee, who held a relatively junior position, denies the allegations, it is understood.
Big Pictures, which launched in 1992, claims to be the world's largest celebrity picture agency, supplying pictures to 40 countries.
Owner Darryn Lyons gave evidence to the Leveson Inquiry into press standards in February. He told the hearing that photographers "didn't know where they stand" when taking images of celebrities.
"We do not know from one day to the next whether they are going to want it or not," he said. It is so ambiguous - we do not know what is right and what is wrong. Fifty per cent of celebrities want to be photographed and they love it but others will pick and choose their terms."