Employer isn't paying my overtime, is this legal?

I work at a tech company in Hyderabad and have been putting in a lot of overtime recently, sometimes up to 20 extra hours a week. However, my employer says they don't pay for overtime and it's part of the job expectation. This doesn't seem fair to me. It's affecting my health and personal life. I'm not sure if this is legal or if I have any rights to claim this overtime pay under Indian labor laws. What should I do next?