This question is based on a social media post of a presumably real situation someone I don't directly know is facing.
Suppose a landlord leases housing to a person, with a requirement in the lease to get a "dog permit" from the landlord to have a dog living in the place, and grants the permit at the time the lease is signed. Then, immediately after the person moves in, the landlord tells them the dog permit has been rescinded, with no prior communication or incident that would have caused a change in circumstances, and threatens the new tenant with eviction if they do not get rid of their pet immediately.
What legal recourse does someone have in such a situation? Are there US jurisdictions where this kind of behavior by the landlord is legal? The person who it happened to belongs to one or more classes likely to be discriminated against, so these antics may be "constructive" to deny housing where the real intent is unlawful discrimination; if so, does that change anything about how the law sees it and how to handle the situation?