Dear Namrata,
You have not mentioned whether your friend is contractual (outsourced) employee. Denial of leave is illegal for any employee whether regular or contractual. Principal employer is responsible to ensure that the labour laws are implemented in right earnest notwithstanding the status of the employees.
Possibly your friend is contractual employee. Possibly that employer, while making contract with the manpower contractor did not make provision of any additional manpower to cater to the absence of employees on account of sickness or authorised leave. Now they are depriving the basic rights of employees.
Tell your friend to talk to HR. However, if your friend adopts collision course, he/she could be removed with just day's notice. Is your friend prepared for this?
If your friend is not much worried of his/her employment then he/she may approach labour officer of the area and explain the problem. But let this not be done without knocking the doors of HR.
Every other day, strange problem of violation of the labour laws comes up in this forum. If what you have written is true then hats off to obsequiousness of that company's HR.
Just recently, I gave a long reply to similar post. You may click the following link to know why is this happening:
https://www.citehr.com/423107-soft-s...ml#post1915976
Ok...
Dinesh V Divekar