Krungthep Thanakom was set up by the Bangkok Metropolitan Administration to oversee its business operations.
The Department of Special Investigation has targeted top city officials, including governor candidate MR Sukhumbhand Paribatra, in its probe of a contract that it contends was illegitimate because it lacked prior approval by the interior minister.
Prapanpong said the deal was a management contract to operate mass transit services and not a state concession as interpreted by the DSI.
He doubted that the Interior Ministry would try to cancel the contract because that would disrupt key transport services and risk the wrath of commuters.