Minn. Stat. § 122A.17: VALIDITY OF CERTIFICATES OR LICENSES.

A rule adopted by the Board of Teaching or the Professional Educator Licensing and Standards Board must not affect the validity of certificates or licenses to teach in effect on July 1, 1974, or the rights and privileges of the holders thereof, except that any such certificate or license may be suspended or revoked for any of the causes and by the procedures specified by law.