An inquiry is under way into security at Birmingham's Council House after protesters burst through the main entrance and occupied the council chamber minutes before a meeting was due to begin.
The incident yesterday involved about 40 residents from the Attwood Green Housing Estate.
They were campaigning in favour of a planning application by Asda, which they fear will be withdrawn if a rival bid by Tesco for a superstore off the A38 Bristol Road is approved.
The council planning committee is expected to back the Tesco scheme next week although a final decision will be taken at a public inquiry.
The Asda scheme for a superstore at Attwood Green has been deemed too large by the council and is likely to be rejected.
City council leader Mike Whitby, deputy leader Paul Tilsley, and Labour group leader Sir Albert Bore were forced to listen to the protesters' spokesman for five minutes before the council chamber could be reclaimed.
Coun Whitby (Con Harborne) said: "While I appreciate the concerns of the residents, I was mildly shocked to discover that they had occupied the council chamber.
"The Council House represents local democracy and it is right that the building should be easily accessed by the public. However, we may need to look at our security."
Council security staff at the main entrance were powerless to act as the protesters ran into the building about 20 minutes before the monthly council meeting was due to begin.
Residents' spokesman Steve Austin rejected a compromise which would have enabled him to meet the three party leaders in a private room.
He said Attwood Green residents were concerned that the regeneration of the former Lee Bank housing estate would be set back if the Asda scheme was dropped.