Basic Salary reduced in Salary structure but Gros salary unchangd

Sub: Basic Salary reduced in Salary structure while Gross salary (CTC) is unchanged. I am working since last 12 years in a public limited company (BSE listed). Now company is going to change the salary structure by reducing the basic salary to 25% of Gross salary, in place of existing basic salary of 40% of gross salary. In both condition the Gross salary is not changed. Existing structure (basic approx. 40% of CTC) Basic Salary : Rs. 15000/- CTC: 4,50,000/- New revised structure (basic approx. 25% of CTC) Basic Salary : Rs. 9,300/- CTC: 4,50,000/- Sir, I am working at the corporate office which dont have any employee union and no any special HR department or HR Head. All decisions are taken by the MD and the GM. Sir, this change is not acceptable to me as it will reduce my PF contribution as well as my Gratuity and my Leave encashment at the time of termination because these all terms are going to be calculated on the basic salary of my salary structure. My questions are: 1) Is my company lawful to do this without taking my (employee’s) prior confirmation/acceptance? can company forcefully apply this change on me? 2) As an employee can I solely deny it? as i told you we dont have employees union. 3) What are the possibilities; what are my rights to get the salary with existing salary structure? Regards Satvekar