24 CFR §290.19

The purchaser of any multifamily housing project shall not refuse unreasonably to lease a dwelling unit offered for rent, offer to sell cooperative stock, or otherwise discriminate in the terms of tenancy or cooperative purchase and sale because any tenant or purchaser is the holder of a Voucher under Section 8 of the United States Housing Act of 1937 (42 U.S.C. 1437f), or any successor legislation. The purchaser's agreement to this condition must be contained in any contract of sale and also may be contained in any regulatory agreement, use agreement, or deed entered into in connection with the disposition.