Withholding of Salary

Hello, My friend works in Mumbai. She started working with a private Indian bank in February. Prior to joining the bank, she furnished all the required details regarding her background verification. However, her salary for February was withheld as the HR said that her reference checks had yielded some discrepancy. However, her salary for Feb was credited in the month of March along with March's salary and nothing was mentioned about it then. However, just before the salary for April was to be credited, the HR called her and asked for contact numbers of the references of her previous employer. The HR manager told her that the reference has not been picking up their phone. This month too, her salary has been withheld and the HR is giving the same reason as before. Also, the HR has barred her from marking her attendance in the workplace. Is the HR right in withholding salary? Shouldn't the background verification have been completed before joining the organisation? What options does she have to remedy this situation?