First the employment offer letter is to be seen about the conditions imposed to accept the employment. If the offer letter states that he is bound to serve the company for a period of three years or to pay the compensation as mentioned in the T&C or offer letter, he may have to comply with the conditions he has agreed and signed.
The subsequent bond may be relating to the training imparted to him by the company which would be a strategy to recover the training expenses, so this if he has accepted and signed, the company will decide about the beneficial situation and may waive one bond at its discretion.
However, let the employee get the confirmation about it in writing and after seeing the contents of the letter by the company further legal action can be decided.