A security employee of the Department of Human Services, as defined in Section 14-110, who is a member of the Teachers’ Retirement System established under Article 16 of this Code may elect to become a member of this System on either June 1, 2001 or July 1, 2001 by notifying the Board of the election in writing on or before May 31, 2001.
     For persons electing to become covered employees, participation in the Article 16 system shall terminate on June 1, 2001, and membership in this System shall begin on that date.
     For persons electing to become noncovered employees, participation in the Article 16 system shall terminate on July 1, 2001, and membership in this System shall begin on that date.