6. The workmen to whom this Act applies are- (a) workmen employed in any employment or class of employment to which the ¹[* * *] Essential Services (Maintenance) Act, 1952, has been declared under section 3 thereof to apply, whether such declaration is or is not subsequently revoked; (b) workmen employed in any factory as defined in clause (j) of section 2 of the ²[Factories Act, 1965]; (c) workmen employed in any mine within the meaning of the Mines Act, 1923; (d) workmen employed in any major port; (e) workmen employed on any estate which is maintained for the purpose of growing cinchona, coffee, rubber or tea, and on which on any one day in the preceding twelve months, twenty-five or more persons have been employed as workmen; (f) workmen employed in any employment specified in this behalf by the Government by notification in the official Gazette.