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I found it. It's part of the 2003 "Citizens’ Personal Protection Act"

Subd. 18. Employers; public colleges and universities. (a) An employer, whether public or
private, may establish policies that restrict the carry or possession of firearms by its employees
while acting in the course and scope of employment. Employment related civil sanctions may
be invoked for a violation.
(b) A public postsecondary institution regulated under chapter 136F or 137 may establish
policies that restrict the carry or possession of firearms by its students while on the institution's
property. Academic sanctions may be invoked for a violation.
(c) Notwithstanding paragraphs (a) and (b), an employer or a postsecondary institution may
not prohibit the lawful carry or possession of firearms in a parking facility or parking area.