Shwetha - Night shift allowance is a benefit extended to an employee for managing the hardship of continuing with odd-office timings.
There are THREE practical thoughts:
1. If COVID-19 pandemic has effected your business operations/ made it infeasible to operate in a night / odd shifts - you may exercise discretion to discontinue shift allowances. But night shift should be disbanded for everyone. These two things should go hand in hand. It will be injustice if employees (or some of them) are being asked to report for work during night or odd shifts and they are not being paid for the hardships caused due to this, even during such times.
2. Adjusting a salary component is something fine - but employees should be kept utmost informed about this through an official letter/ e-mail communication. New salary structures may be provided to the employees and sign-off should be obtained from them. A clear FAQ document should be prepared and shared with all the effected employees alongwith such communications.
3. The above applies to all the salary/ designation bands in an Organization - please see, if your organization can reduce complexity of the situation and bring uniformity in pay policies for all the levels.