As a Salesforce administrator, you can control users' access to the discount charge field using the field-level permission. If user does not have the Read access to the Discount field of the Quote Rate Plan Charge object, the Discount field does not show in the Choose Product and Charges page, and the user is not able to edit discount charge values.

The Discount field access also controls adding, updating, and removing custom tiers.

To restrict user's access to charge discounts, revoke the field-level access to the Discount (zqu__Discount__c) field of the Quote Rate Plan Charge (zqu__QuoteRatePlanCharge__c) object for the user. See the Salesforce documentation for the steps.

To restrict all users from accessing charge discounts, use the quote setting, Disable Discounting, in Zuora Config. See Enable Additional Price Discounts for detail information.