I have no other points to make than what have been put by Mallik and Simhan.It is a matter of bad HR culture which prevents one from joining another company. Every one (including the one who makes an employment Bond) knows that bond is invalid and compelling an employee to stay or restricting an employee from joining a competitor is illegal, but still the HR is forced to make such rules.
In a similar case with one of my friends, I had advised him to get a bond from the employer stating that if the employer terminates his service (which often happens with IT companies or companies which entirely depends on the money of other countries- as is called the MNC- when a bomb is exploded or a small bank is wound up in the US or UK!) he should also be given the same bond amount, and the employee did so, but instead of giving an undertaking that he would not be terminated he was relieved without any condition.
Therefore, in such situations, it is the bargaining or the interference of a mediator/ conciliator that works rather than the logic. Therefore, find out some body who can talk to the HR or person who is to take the final decision and proceed. It is the human values which are more important in the present time HR and it is claimed that present HR is some thing which is great and is entirely different and very vibrant and is not the same old Personnel Management. But I have noticed no change except a change in the name or title though the values have come down drastically and the human exploitation has become more and more significant.
Madhu.T.K