Do emotional support animal letters work in every state?

The short answer

The protection is federal, so the underlying right exists in every state. The document is not, because it rests on a clinician licensed in one particular state. A letter written by a clinician licensed in Ohio is a strong document in Ohio and a questionable one in Arizona, and a housing provider entitled to reliable documentation is entitled to notice.

What varies between states

• Whether the state has its own assistance animal statute. Seven do, and in those states the documentation standard is written down rather than inferred.
• Whether a relationship rule applies. Arkansas, California, Iowa, Louisiana and Montana require a clinical relationship of at least thirty days before documentation issues.
• Which agency takes a complaint, and whether the state has one at all. Two states have no fair housing statute of their own.
• What the state landlord-tenant law says about deposits and non-refundable fees, which since May 2026 is what decides the pet fee argument.

What does travel

The reasonable accommodation duty itself, and the private right of action that enforces it. Those are in the statute and do not change at a state line. What changes is how well your particular document supports the claim once you are on the other side of it.