Section 6(b) in The Calcutta Municipal Corporation Act, 1980
(b)so often as a vacancy in the office of the Mayor or the Chairman, as the case may be, occurs by reason of death, resignation, removal or otherwise and within one month of the occurrence of such vacancy, one member to be the Mayor or the Chairman, as the case may be, who shall assume office forthwith after taking such oath of secrecy as may be prescribed.
