Initially, you may see a trivial example "Regional Planning" in Section 3.4 in the book:
Introduction to Operations Research, 10 ed., by Frederick s. Hiller and Gerald J. Lieberman, 2015,
where a fair use of water is modeled by constraints coming from such requirement "To ensure equity between the three entities (organizations), it has been agreed that every entity (enterprise/ organization) will plant the same proportion of its available irrigable land."