I recently discovered that Wisconsin Tax Appeals Commission Rulings and Orders are now available in full text on Wisconsin.gov. The Tax Appeals Commission (TAC) is an independent state agency that was created by the Wisconsin State Legislature to hear and determine disputes between taxpayers and the Wisconsin Department of Revenue and, in some limited instances, the Department of Transportation. The TAC also resolves tax disputes in the areas of individual income, corporate income, county sales tax, cigarette use, homestead credit, and many more. The TAC is the successor to Wisconsin Board of Tax Appeals.
TAC decisions back to 1984 are browsable alphabetically by Petitioner name on Wisconsin.gov. A chart of decisions on frequently addressed issues is also available. Decisions from 1999-2021 are also searchable by keyword on the Wisconsin State Bar website. Earlier decisions from 1939-89 are available in print at the UW Law Library.
For further Wisconsin tax law research, consult the Wisconsin Topical and Court Case Index from the Department of Revenue. It includes references, by tax type and alphabetically, to Wisconsin statutes, administrative rules, tax releases, private letter rulings, Wisconsin tax publications, Sales and Use Tax Reports, Wisconsin Tax Bulletin articles, Attorney General Opinions, and court decisions of the TAC and the Wisconsin courts. See also Publication 507 for information on how to appeal a WI DOR decision to the Tax Appeals Commission,