How can you negotiate with employer you recently joined finding out that the salary package it has offered does not match with grade offered

Do you know of other employees who have experienced similar issues?

First, gather your evidence. Don't rely on feelings. You need concrete proof.

Don't raise this issue in a group setting. schedule a one on one meeting with your manager or HR representative.

See if you have already joined. I dont see any scope after that. Never seen anyone increasing salary post joining. May I know what the difference in the range ?