https://www.keka.com/library/minimum-wages/tamilnadu
Pl.go thru' the contents of the above link.
As far as I know there is strict rule prescribing any %age of HRA as part of salary under TN Shops & Estts.Act. And even under Minimum Wages notified by the TN Govt. there is no such a stipulation but there is Basic & DA part of minimum wages, no HRA stipulated. However any attempt affecting the present emoluments will be contentious issue and HRA one such a matter and an attempt to reduce the %age thereof will not be acceptable by the employees. May be there should be an agreement or Letter of appointment where these rates could have been mentioned. If so it's not possible to effect an unilateral action my employer without the formal approval of all employees concerned.