Membership is open to the current and retired employees of Alliant-Energy Corporation, its successors, American Transmission Company (ATC), ITC Midwest, NextEra Energy / Duane Arnold Energy Center, Flexsteel, Georgia Pacific, and Mystique Casino. Approved businesses, owned by company employees, that are included in ACUs field of membership are as follows: Busy Bee Tree Service and Advanced Technical Solutions. Membership also includes the employees spouses, children, sons and daughters-in-law, grandchildren, mother, father, mother-in-law, father-in-law, brothers, sisters, grandparents, grandparents-in-law, brothers and sisters-in-law, uncles and aunts, nieces and nephews, and great grandchildren. "Once A Member, Always A Member". There is no employment nor residency requirement to maintain membership.