What is the ruling on obtaining a loan from a bank with an end-of-service bonus as collateral?

If the loan is a Qard Hasan (a benevolent loan) that does not stipulate an increase in repayment, then it is permissible. The bank's request for the end-of-service bonus as a guarantee for its dues is also Islamically permissible as a legitimate guarantee. However, if the loan is to be repaid with a stipulated increase, then it is Riba (usury) and Islamically forbidden. It is not permissible to engage in it except in cases of extreme necessity.