Section 2(1)(b) in The Essential Services Maintenance Act, 1968
(b)"strike" means the cessation of work by a body of persons employed in any essential service acting in combination or a concerted refusal or a refusal under a common understanding of any number of persons who are or have been so employed to continue to work or to accept employment, and includes-(i)refusal to work overtime where such work is necessary for the maintenance of any essential service ;(ii)any other conduct which is likely to, result in, or results in, cessation or substantial retardation of work in any essential service.