Dear friend from HR Revolution Services,
To my knowledge, there is no legal bar to the collection of a security deposit from employees if the nature of the job requires handling cash and other valuables in the business transactions of the organization. Therefore, the fairness of such a practice depends entirely upon the nature of the responsibilities of the job position. Certainly, it will be mandatory to pay interest at the current bank rate when the contract comes to an end.
In the case of companies registered under the Companies Act, 2013, if I remember correctly, the collection of a security deposit is permissible under rule 2(1)(c)(x) of the Rules, 2014. However, it shall be a non-interest-bearing deposit not exceeding the concerned employee's annual salary. For further clarification, you may refer to the Companies (Acceptance of Deposits) Rules, 2014.
Regarding the present thread, if the intended security deposit is purely for the purpose of compelling the FTC employee to serve the entire tenure of the contract, I think it will not be fair, and it would also constitute an illegal deduction from salary under the Payment of Wages Act, 1936, and the Code on Wages, 2019.