Does a Massachusetts landlord have to approve a Section 8 applicant? No, so long as the reason for the rejection is not the Section 8 voucher. Landlords are required by state law to participate in the Section 8 program, if a Section 8 voucher holder is the most qualified applicant. That does not mean you have to approve the rental application for anyone just because they have a Section 8 voucher. You can reject their application for the same reasons you would reject other applicants, so long as the reason is genuinely unrelated to their receipt of public assistance.
Landlords in Massachusetts may be obligated to modify their "no pets" policies to allow a resident to keep an animal that does not meet the Americans with Disabilities Act (ADA) definition of "service animal." This post will clarify the status of other types of animals that may assist individuals with disabilities, such as emotional support/companion animals, and their status under Massachusetts Fair Housing laws.