Airport operator BAA has complained that immigration queues at Heathrow are "unacceptably" long, just weeks before the Olympic Games are due to begin.
Last week some passengers faced waits of up to two-and-a-half hours - raising fears that the immigration system may not be able to cope with the arrival of thousands of athletes.
BAA said the Home Office had promised all Border Force desks at Heathrow would be manned during the peak Olympics arrival times.
But it added that the Home Office should be "delivering a good experience for regular passengers as well as Olympic visitors".
According to the Daily Telegraph there were half-mile queues at Heathrow's Terminal 4 last Friday, while pictures in the paper showed empty immigration desks.
The Immigration Service Union, which represents 4,500 border staff, told the paper that the present problems were being made worse as only about half the current workers were fully trained to allow passengers from anywhere in the world entry.
A Border Force spokeswoman said the queues at Heathrow had been "less than an hour" and that extra staff had been deployed to deal with them.
She went on: "We are fully prepared for the busy Olympic period and will be implementing our well-rehearsed plans.
"This includes staffing all immigration desks at key ports whenever necessary during the peak Olympic and Paralympic arrivals period."