Hi Deepak Chandran,
I may not be familiar with the country/city law in your region. Though your query is somewhat not clear for me, but I'd like to share some inputs and I hope I understand your point..
1. Basically, an employee cannot just work whenever he/she likes. There could be reasons why he/she likes to work. My point here, there is a difference between "like" and "need". Does he/she like/want to work or does he/she needs to really work during off days?
2. Initially the superior/department head must be responsible for ensuring that his/her subordinates do not work during off days. Depending on work load or urgent business needs or submission of project on a deadline, which will likely be seldom I guess, this will be a case-to-case basis.
3. HR must be the one controlling the work during off. Once approved by the department head that there is a need to work during off days, the HR is then the final one who needs to verify the justificaiton of such instance. Remember, off day work involves cost and HR knows well that cost should be controlled.
4. We say there is a need to work, is his/her compensation paid with OT or just a normal staff with fixed salary? If with OT, depending on the law in your region, an OT pay is a MUST with compensatory/alternative holidays. Again, this depends on your region labour rules. If he/she is a staff, a rate per day with double-payment of the basic salary may be provided. But my question here is that, do you have any policy that pertains to any off-duty works? Some companies may have what they call the "holiday duty bill" that is based on designation-leveling. If you do not have the policy yet, kindly prepare for future improvement plans and then have it approved by HR.
Anyway, with all the explanations, I still believe that a company has to have a strict policy to not allow any off day works. Everyone should be entitled to at least 1 day off for every 6 days continuous duty.
Good luck!