An investigation is under way into the handling of airside passes at London's Heathrow Airport.
The passes allow people to access secure areas of the airport as well as access to aircraft and other equipment.
The inquiry began after two women were arrested over alleged fraud.
The women, who are aged 20 and 24 and from Surrey, were held on suspicion of money laundering and fraud on 3 August after money was taken from a bank account.
It is understood that the fraud investigation then triggered an inquiry into airside passes.
Scotland Yard stressed that there is no counter-terrorism link and that there is no evidence that staff airside passes have been sold.
A spokesman for Heathrow Airport said: "Our top priority is the security and safety of our passengers and colleagues and we have taken appropriate action until the investigation is completed."