When is itr filing compulsory

Dear Experts, i need your help in order to know when the filing of itr compulsory for a salaried employee.

e.g. A person whose gross income is 3lakh and after the exemption of HRA it comes donw to 1.5 lakh (on which there is no tax liability) in this case is it mandatory to file itrt. Please note that the income becomes non taxable after the exemption of HRA ONLY and not the deductions under section 80C. If the deductions under sec 80C are applied it will further bring down the taxable income from 1.5 lakh to 1lakh.

Thanks

Aman