As a matter of Statutory requirement you must go through Factories Act, Rules, EPFO, ESI Act.
Please check the concerned website for necessary guidance for PF EPFO <link updated to site home> please check it from here.
For esi employers there is a link available ESIC <link updated to site home> please check it from here.
For Bonus, Gratuity, Retrenchment Benefits, etc please refer the Payment of Bonus Act, Payment of Gratuity Act, ID Act, etc. respectively.
6th September 2011 From India, Kumbakonam