Did you get the letter last week? The reason I am asking this is because last week the Economic Times carried an article which stated that one of the Birla companies has added this clause in the offer letter because they believe that it takes 3 months to close a recruitment and lots of time gets invested into it apart from money. So, if one refuses the offer, then the company is 3 months behind for a person to join. I believe that some smart HR professionals would have immediately wanted this clause to be added. But, what one did not think about is whether it's valid. As per law, if it's accepted, then it is valid since you are creating a contract. However, if you default and do not join, does the company have the patience to sue you? My honest answer would be no. Apart from sending you notices and maybe publishing in the newspaper a summons to court like TCS used to do and fighting the case, is not only time-consuming but also costs money. At some point, they are going to look at the ROI and find that it is negative. Additionally, the legal department has much more important work to do.
And what happens if one goes to court? Once the judgment is given, the candidate can opt for paying the money in installments of INR 500 every month, and the court will agree. However, the candidate may default, and the company will hire a lawyer to send a notice of default. The lawyer's cost would be between INR 5k to 10k for that single notice.
Before incorporating any clause, many companies do not think whether such a clause is legally tenable and also practical to implement. The CEOs can propose, but it's the HR's duty to enlighten the CEO that it's not practical and does not make commercial sense.