Louisa,
I agree that the MC should always do due diligence. However, they may have been instructed to send the letter by the Board - hence, the issue is likely with the Board.
Per the
The Fair Housing Act, The Act protects people from discrimination when they are renting, buying, or securing financing for any housing. The prohibitions specifically cover discrimination because of race, color, national origin, religion, sex, disability and the presence of children.
Per
this 2015 article from a legal firm:
While each situation is unique and must be evaluated individually, in virtually all cases the association will NOT be able to enforce these restrictions against a group home because of the provisions of the Federal Fair Housing Act, 42 U.S.C. ยง 3601
If you are involved in the situation, I wouldn't run to HUD just yet. Try and resolve at the lowest level. Contact the Board and simply make them aware that such a demand is likely a violation of the Fair Housing Act and encourage them to seek a legal opinion vs. opening the Association up to a potential legal action.