Airport operator BAA has said passport queues have been "unacceptably long" during peak periods in the last few days.
The complaint comes after a visit from Keith Vaz, chairman of the home affairs committee, where there were queues of more than an hour for non-EU passengers and half the passport desks were closed, the Guardian reports.
Travellers also face delays getting into London with the closure of the M4 motorway for repairs, see previous story.
A Border Force spokesperson said: "Keith Vaz is incorrect. Queues at Terminal 4 remained under an hour at all times. Staff were quickly redeployed and more than 80% of desks were open to process passengers as quickly as possible."
BAA said: "Immigration waiting times for passengers during peak periods at Heathrow in the last few days have been unacceptably long and the Home Office should be delivering a good experience for regular passengers as well as for Olympic visitors."
