A Calcutta Municipal Corporation engineer was showcaused on Friday after he went to demolish an illegal building at Ashwininagar in Jadavpur and was stopped by the local Trinamul councillor.

Tapan Dasgupta, the councillor of Ward 95, said the civic body first needed to demolish the house of minister Aroop Biswas in New Alipore before trying to pull down any illegal building in the colony areas.

Asked why he had mentioned minister's Biswas's name, the councillor later said: "I only tried to cite an example. The plot on which Biswas's three-storey house stands is part of a colony area. Like other plots in the area, it has been developed illegally, too. If the CMC wants to demolish illegal buildings in colony areas, they need to demolish houses of powerful men first."

The minister refused to comment on the issue.

"The assistant engineer did not take my permission or that of the municipal commissioner before setting out for the demolition," mayor Sovan Chatterjee said in the evening.

"The high court had in 2014 given some privileges to buildings in colony area because of the sheer number of people living there. So, it was wrong on the part of the engineer to set out for the demolition without consulting us."

The assistant engineer has been asked to state who had given him the permission for the demolition.

Councillor Dasgupta, who was sitting in front of the illegal building when the demolition squad turned up, said almost all structures in Ashwininagar, "just like any other colony area", are unauthorised. "I raised that issue with the assistant engineer."

When the members of the demolition squad tried to enter the building, Dasgupta stopped them, asking who had sent them. Sources said the assistant engineer leading the team showed the councillor "valid" papers. "But the team faced stiff opposition and had to return. Half an hour later, the engineer was showcaused," a source said.