Calculation of Gratuity during COVID 19 where Management is decided to cut 10% Salary for all the employees

Greeting to All: Hope all are safe and staying at Home. Seek you clarifications on the following:
Sub: Calculation of Gratuity Amount Retirement
1. One of our employee is getting retired during May,2020.
2. Due to the present situation our Management is decided to cut 10% Salary for all the employees.
3. In the case of retired employee for eg. His present Basic of Rs.20,000/- will be Rs.18000/-. (Salary Revision given during April 2019)
4. He is having 25 Years of Service.
5. At the time of Gratuity we have take Rs.20000/- as Basic or Rs.18000/- .
Seek your valuable guidance.

How Gratuity is Calculate
The gratuity amount depends upon the tenure of service and last drawn salary. It is calculated according to this formula: Last drawn salary (basic salary plus dearness allowance) X number of completed years of service X 15/26.
According to this formula, the time period of over six months or more is considered as one year.
With Rs20,000 as salary(without taking DA) it works out to Rs 288000 Appx.
With DA it will increase
if you cut his salary to Rs18000 he will get only Rs175000 appx
It will be unfair to reduce his salry and give him lesser gratuity.
In context of directives passed with regard to Covid and Employees, such curtailment will be questionable.