MPs have raised concerns that Heathrow will not be able to cope with the large number of people due to arrive in London for the Olympic Games.
The House of Commons Culture, Media and Sport committee said it was worried that the airport was not prepared for the "huge number of competitors, Olympic family and visiting tourists" due to descend on it in the summer.
In a letter sent to culture secretary Jeremy Hunt, the MPs warn that long queues could develop at immigration and that insufficient funding had been made available to the UK Border Agency to ensure all the passport stations would be open.
"While visiting tourists will understand that the Olympics is a busy time, if the wait is in excess of an hour then it may deter tourist from returning," the letter said.
"The second impact may be that planes cannot unload their passengers into the terminal due to capacity being exceeded. This would lead to circling in the air, planes being left on runways or planes blocking gates."
The letter adds: "Furthermore, the proportion of passengers entering Heathrow from outside the EEA may be significantly higher than usual. Again, this takes longer to process through immigration."