You can add any clause to a license. JSON's license is famous for adding "The Software shall be used for Good, not Evil."
It probably makes it non-open source and non-free according to OSD and FSF
https://opensource.org/docs/osd "The license must not restrict anyone from making use of the program in a specific field of endeavor. For example, it may not restrict the program from being used in a business, or from being used for genetic research."