Delta Air Lines has said it is working with the FBI after sewing needles were found in food on four US-bound flights from Amsterdam on Sunday.
One passenger was injured after the needles were found in sandwiches made by the airline's Amsterdam caterer, Gate Gourmet.
The airline said that the FBI and Netherlands officials are investigating the incidents.
It said: "Delta is taking this matter extremely seriously and is cooperating with local and federal authorities who are investigating the incident.
"Delta has taken immediate action with our in-flight caterer at Amsterdam to ensure the safety and quality of the food we provide onboard our aircraft."
One person on a flight to Minneapolis was injured but declined medical treatment.
A suspected sewing needle was also found in a sandwich by a passenger on an Atlanta-bound flight. A US air marshal found another while flying on another Atlanta-bound flight.
Another apparent needle was found aboard a Seattle-bound flight in a sandwich that had not been served.
Gate Gourmet spokeswoman Christina Ulosevich said the company has received no reports of similar incidents on any of the other airlines it serves out of Amsterdam.
She said the company did not yet know how the needles got into the sandwiches.
Gate Gourmet said: "We take this matter very seriously and we have launched our own full-scale investigation."
It also said it was "heightening our already stringent safety and security procedures, to prevent any recurrence".