Section 55 of the Act lays down that the periods of work of adult
workers in a factory each day shall be so fixed that no worker shall work for more than 5 hours
before he has had an interval for rest of at least half an hour. The Chief Inspector of Factories
can exempt any factory from this provision so however that the total number of hours worked
by a worker without an interval does not exceed six.
Section 56 of the Act stipulates that the period of work of an adult worker in a factory
shall be so arranged that, inclusive of his intervals for rest under Section 55, it shall not spread
over more than ten and half hours on any day. The Chief Inspector, may, however, increase the
spread over upto twelve hours on specific grounds
So this makes it clear that such 12 hour shifts will not be permissible without specific permission of appropriate Labour Authority.