Landlord Accountability Act of 2023 This bill prohibits housing discrimination based on income, provides protections to tenants of certain federally assisted housing, and establishes a low-income housing maintenance tax credit for eligible landlords. Specifically, the bill prohibits discrimination in rental housing and residential real estate transactions based on an individual's source of income and provides for penalties. Protected income sources include housing vouchers and rental assistance, rental and homeownership subsidies, Social Security and disability income assistance, and spousal and child support. Additionally, landlords are prohibited from taking or failing to take certain actions with the intent to make a unit ineligible to receive Department of Housing and Urban Development (HUD) assistance. Landlords that violate this prohibition are subject to penalties and may be sued by harmed tenants. The bill further prohibits property owners of certain multifamily housing projects from intentionally leaving a unit vacant for more than 60 days. Property owners that violate this prohibition are subject to penalties. The bill also provides protections to tenants of multifamily housing projects, including by requiring HUD to increase the staffing level for the Multifamily Housing Complaint Line and to create a Multifamily Housing Complaint Resolution Program. In addition, HUD may provide grants to develop, expand, and assist tenant harassment prevention programs. Finally, the bill establishes a tax credit for qualifying landlords that is equal to the landlord's annual low-income housing maintenance expenses. To qualify, a landlord must have addressed within 30 days any relevant complaints filed under the complaint resolution program.