In any proceeding involving Sec. 458.26, a trusteeship established
by a labor organization in conformity with the procedural requirements
of its constitution and bylaws and authorized or ratified after a fair
hearing either before the executive board or before such other body as
may be provided in accordance with its constitution and bylaws shall
be presumed valid for a period of 18 months from the date of its
establishment and shall not be subject to attack during such period
except upon clear and convincing proof that the trusteeship was not
established or maintained in good faith for purposes allowable under
Sec. 458.26. After the expiration of 18 months the trusteeship shall be
presumed invalid in any such proceeding, unless the labor organization
shall show by clear and convincing proof that the continuation of the
trusteeship is necessary for a purpose allowable under Sec. 458.26.
