Credit unions which are exempt from the Wisconsin franchise or income tax under the provisions of Ch. 71, Wis. Stats., should file Form CU instead of filing a Wisconsin corporation franchise or income tax return, Form 4 or 6. Thereafter, the credit union need not file a corporation tax return (Form 4 or 6) or Form CU for any subsequent year unless re¬quested to do so by the Department of Revenue or unless in a subsequent year the credit union acts as a public depository.
Credit unions that do not derive income from public deposits are exempt from the Wisconsin tax on unrelated business taxable income, as computed under section 512 of the Internal Revenue Code.