Minn. Stat. § 333.41: TRADEMARKS OF WORKERS' UNIONS.

When any person, or any association or union of workers, shall have adopted or used any label, trademark, term, design, device, or form of advertisement for the purpose of designating, making known, or distinguishing any product of labor as having been made, produced, prepared, packed, or put on sale by such person, association, or union, or by a member thereof, it shall be unlawful to counterfeit or imitate the same, or to use, sell, offer for sale, or in any way utter or circulate, any counterfeit or imitation of any such label, trademark, term, design, device, or form of advertisement.