Under Section 57(1), the employment of contract labour is prohibited in which of the following?

Section 57(1) prohibits the employment of contract labour in the core activities of any establishment. However, the principal employer may engage contract labour in a core activity if the normal functioning is such that the activity is ordinarily done through a contractor, or the activity does not require full-time workers for the major portion of the working hours, or there is a sudden increase in the volume of core-activity work needing completion in a specified time. A designated authority advises whether an activity is core.