No employer, who proposes to effect any change in the conditions of service applicable to any workman in respect of any matter specified in the Fourth Schedule, shall effect such change,—
(a) without giving to the workmen likely to be affected by such change a notice in the prescribed manner of the nature of the change proposed to be effected; or
(b) within twenty-one days of giving such notice:
Provided that no notice shall be required for effecting any such change—
(a) where the change is effected in pursuance of any 2 [settlement or award]; or
(b) where the workmen likely to be affected by the change are persons to whom the Fundamental and Supplementary Rules, Civil Services (Classification, Control and Appeal) Rules, Civil Services (Temporary Service) Rules, Revised Leave Rules, Civil Service Regulations, Civilians in Defence Services (Classification, Control and Appeal) Rules or the Indian Railway Establishment Code or any other rules or regulations that may be notified in this behalf by the appropriate Government in the Official Gazette, apply.