Police said on Wednesday they had arrested a British Airways reservations agent in northern England on suspicion of raising funds for terrorism.
The 30-year-old man was arrested by detectives from the North East Counter-Terrorism unit at the call centre in Newcastle last Thursday.
Detectives have been granted extra time to question him and he remains in custody at a police station in central London.
"We can confirm that one of our employees was arrested at our Newcastle office last week," a British Airways spokesman said.
He said the employee, who dealt with bookings, would not have been subject to security checks as he would have had no access to any sensitive information.
The Sun newspaper said the fundraising was connected to raising cash for an attack, possibly on a plane, but a police spokeswoman said that was speculation.
Britain raised its threat status in January to "severe," the second-highest level, meaning an attack was thought to be highly likely, although there was no intelligence that anything was imminent.