A teacher being a member of the Manitoba Teachers’ Society Committee or of the Executive Committee or any branch thereof, or of any special committee of the Society, or being appointed an official representative or delegate of the Society, or any branch thereof, and being authorized by the Executive Committee, shall be excused from school duties for either purpose or both purposes providing that collectively the total number of days does not exceed eighty-five (85) days with a maximum of six (6) teachers being absent on any occasion. On two (2) occasions per year, more than six (6) teachers may be absent subject to substitute teachers being available. The cost of providing a substitute teacher salary must be paid by the Society. No additional leave of absence within this clause will be available except with the consent and approval of the Board. In all cases, the teacher shall notify the Board thereof prior to taking such leave.