Travelers using American airports are facing a new obstacle with Transport Security Administration (TSA) officials asking them to remove snacks and powders from their carry-on luggage.

The latest step in the ever-tightening security arrangements surrounding travel in the US is not an official policy but is being enforced by officers at many airports across the country.

Requests to remove snacks and powders have been made at a number of major hubs including Newark, Atlanta, Los Angeles, New York and San Francisco, leading to security delays as the US tourism season gathers pace. The changes have seen passengers told to put food they had bought to eat onboard the aircraft into separate bins for further inspection.

On at least one occasion the delay has been long enough to cause a passenger to miss a flight.

According to the TSA, food in carry-on bags can make it harder for bags to be screened. Tighter rules have also seen passengers required to put powders such as those used to make up energy drinks into an individual bin. Passengers with large quantities of powder are advised to pack it into their hold luggage.

The TSA’s official line is that it is constantly changing security methods to tackle what it describes as an evolving terrorist threat.