Transferred Employees Formalities

Dear All,
I am working in a retail sector, (under Bombay shop & establishment act, Maharashtra). Few of our employees were transferred to another branch in the same city, in mid of the month. My queries are:
1) From where do the salary of the that month should be processed ? (we process payroll branch wise & not centralized)
2) Should we issue transfer letter, to be safe in case?
Thanks in advance

1) From where do the salary of the that month should be processed ? (we process payroll branch wise & not centralized) - If payroll is processed branch wise then why process the salary from date of joining in new branch
2) Should we issue transfer letter, to be safe in case? - If transfer is for longer duration then its better to issue transfer letter else deputation letter will serve the purpose.