The United States' latest directive on airline security is causing concern among airlines.
The directive is the latest in a series of attempts to tighten air security
Carriers including Qantas and British Airways said they would comply with the demand, issued by the US Transport and Security Administration (TSA), just before Christmas, that passengers are asked not to congregate near the planes' toilets.
A BA spokeswoman said the airline was aware of the requirement and was happy that current procedures adequately covered it.
But a BA insider told the Times newspaper: Queueing is a great British tradition. How on earth are we supposed to organise trips to the loo?"
"Should we make people put their hands up or have a ticket system like the deli counter at Tesco's? It would be unworkable to stop passengers forming queues outside toilets."
Australia's Deputy Prime Minister and Transport Secretary, John Anderson, said he was "surprised" by the directive, which he described as "a little bit hard to handle".
It is the latest in a series of moves by the US aimed at tightening air security in the wake of the September 11, 2001 attacks.
Darrin Kayser, a spokesman for the TSA - part of the US Department of Homeland Security - told BBC News Online that passengers could still queue for the toilet, but that congregating in groups would be discouraged.
He said it was up to flight crews to distinguish between "politely waiting for the toilet" and huddling.
A Qantas spokesman said the airline did not expect the directive, which will be explained in a pre-flight announcement, to create any significant upheaval for their passengers, but that it would be monitored during flights.
The chief executive of the Board of Airline Representatives in Australia, Warren Bennett, said he thought the move gave the impression "paranoia is taking over".
"Passengers are caught between a rock and a hard place. On one hand, they are advised to move around an aircraft during flights for health reasons; but now they are being told not to congregate. It doesn't make any sense," he said.
Mr Anderson said the directive would have to "be handled the right way".
Mr Kayser, the TSA spokesman, responded to the suggestion that the directive could pose major disruption to passengers in the hands of over-cautious flight attendants by saying that they had a responsibility to ensure their own safety.
"We frequently say security is not a spectator sport... we can't be successful about stopping terrorism without everyone playing a role," he said.