Share one single withholding tax classification with multiple BUs

Summary:

This would be a fundamental question, but like to get some advices from the experts.

I like to share one single withholding tax rate and the tax classification code among multiple business units within the same legal entity.

However, when I came up to try to assign the Bus in Direct Tax Rate Rules of Manage Withholding Tax Classifications, I do not think that I can assign the same tax classification code to multiple business units.

I just expect that the same withholding tax classification code can be share by multiple business units within the same legal entity.

This question has come out maybe I might be missing some basic points.