Are you running a company or a firm?
Are you the owner/proprietor or whether the firm is a partnership firm?
What is the rule your company states about it.
You cannot decrease the basic salary or change the structure of salary from the one what you have already circulated in the employment offer letter.
You have to incorporate a change in the company policy in this regard and an effective notification is to to be promulgated in this regard after the decision about this has been taken in the company following the procedures in this regard.
Discuss with your auditor and company's legal adviser before taking any such decision