It shall be unlawful to deny any person access to or membership or participation in any multiple-listing service, real estate brokers’ organization or other service, organization, or facility, relating to the business of selling or renting dwellings, or to discriminate against him in the terms or conditions or such access, membership or participation, on account of race, color, religion, sex, familial status, national origin, disability, marital status, or source of income.