To my knowledge, Night Shift Allowance is not statutory. But it has become conventional either to provide some refreshments by the employer or to pay some fixed amount in lieu there of in view of the physiological negative impact likely to occur due to working at night. Medical research has proved that continuos sleepless night work certainly affects "the circadian rhythm" of our body. Therefore, legal or not, night shift allowance would be essential from the point of view of health of such employees who are frequently required to work during nights. The internal economies accrued to the employers through continuous operations would also justify this head of allowance.