18-125-103 Me. Code R. § 9
Records required to be retained pursuant to the terms of this Rule must be retained for the same time period as all other records are required to be kept for the applicable tax. Title 36 M.R.S. §135 requires that records pertaining to the Maine Income Tax (36 M.R.S., Part 8), the Maine Estate Tax (36 M.R.S., Chapters 575 and 577) and the Maine Mining Excise Tax (36 M.R.S., Chapter 371) must be retained as long as is required by applicable federal law and regulation. Records pertaining to the Special Fuel Tax user reports filed pursuant to 36 M.R.S. §3209(2) and the International Fuel Tax Agreement must be retained for at least 4 years. Records pertaining to all other taxes imposed by Title 36 of the Maine Revised Statutes must be retained for a period of at least 6 years. All records must be kept in such a manner as to ensure their security and accessibility for inspection by the Assessor.
18-125 C.M.R. ch. 103, § 9