law: Indian Ports Act, 1908
  34. Variation of port-dues by Government 
  
  
  The Government may after consulting,- 
  (a) in case of ports other than major ports, the authority
  
  appointed under section 36;
  (b) in case of major ports, the Authority constituted under
  
  section 47A of the Major Port Trust Act, 1963, exempt, subject to such
  
  conditions, if any, as it thinks fit to impose, any vessel or class of vessels
  
  entering a port subject to this Act from payment of port-dues and cancel the
  
  exemption, or may vary the rates at which port-dues are to be fixed in the
  
  port, in such manner as, having regard to the receipts and charges on account
  
  of the port it thinks expedient, by reducing or raising the dues, or any of
  
  them or may extend the periods for which any vessel or class of vessels
  
  entering a port shall be exempt from liability to pay port-dues:
  Provided  that the rates shall not in any case exceed
  
  the amount authorized to be taken by or under by or under this Act.]