Olympic windsurfing champion and IOC member Barbara Kendall has described Heathrow Airport as a "nightmare" less than two months out from the London Games.
The transport hub has been widely panned in recent months for struggling to cope with passenger numbers at immigration gates.
New Zealander Kendall is believed to be the first IOC member to publicly criticise Heathrow, which is set for a surge in passenger numbers before and after the Olympics from July 27th to August 12th.
Kendall tweeted "Heathrow Airport Immigration is a nightmare it took her 2 hours to get through and it is not Olympic time yet."
The five-time Olympian's complaints came as London's underground train network has buckled over the past week following a run of warm weather.
Sir Keith Mills, deputy chairman for Olympic organisers LOCOG, said this month that London's reputation was being undermined by the chaos at the world's busiest international airport.
Heathrow will experience the busiest day in its history on August 13 - the day after the Olympic closing ceremony.
The airport normally averages 95 thousand departing passengers a day but will have to handle 138 thousand on that day.
Airport bosses and the British government have promised they will draft in extra staff at passport control for the Olympics with Heathrow the main gateway for the Games.