Same position with different salaries are called grading depending on the qualification, experience, skill and Nationality. You should have signed a contract with your Company in which you would have agreed your remuneration. The company should have submitted a copy of the same in the Labour Dept. Increasing the salary is totally up to your Company and Labour Department will not be able to do anything in this case. It will be better to talk to the GM for an increase or request for an NOC to find a good job and transfer and if not possible quit the job and go home.