law: Company Secretaries Act, 1980
  13. Resignation of Membership and Casual Vacancies
  
  (1) Any member of the Council may at any time
  
  resign his membership by writing under his hand addressed to the President, and
  
  the seat of such member shall become vacant when such resignation is notified
  
  in the Official Gazette.
  
  
  (2) A member of the Council shall be deemed to have vacated his seat if he is
  
  declared by the Council to have been absent without sufficient excuse from
  
  three consecutive meetings of the Council or of any of the Committees which has
  
  been constituted by the Council and of which he is a member or if his name is,
  
  for any cause, removed from the Register under the provisions of section 20.
  (3) A casual vacancy in the office of a member of the Council shall be filled
  
  by fresh election from the constituency concerned or by nomination by the
  
  Central Government, as the case may be, and the person elected or nominated to
  
  fill the vacancy shall hold office until the dissolution of the Council :
  Provided that no election shall be held to fill
  
  a casual vacancy occurring within six months prior to the date of the
  
  expiration of the term of the Council, but such a vacancy may be filled by
  
  nomination by the Central Government after consultation with the President of
  
  the Council.
  (4) No act done by the Council shall be called
  
  in question on the ground merely of the existence of any vacancy in, or defect
  
  in the constitution of, the Council.