(1) Beginning July 1, 2010, the retirement system may determine a separate employer contribution rate for members who first became members on or after July 1, 2010 and before February 1, 2018. Except as provided in this section, the retirement system shall determine the separate employer contribution rate in the manner prescribed in section 41.

    (2) Beginning February 1, 2018, the retirement system shall determine a separate contribution rate for members who first became members on or after February 1, 2018. Except as provided in this section, the retirement system shall determine the separate contribution rate in the manner prescribed in section 41, except that any increase or decrease in the unfunded actuarial accrued liabilities associated with members who first became members on or after February 1, 2018 must be amortized on a 10-year level-dollar schedule with a new contribution rate calculated for each year.

    (3) All normal cost and any unfunded actuarial accrued liability contributions as determined under subsection (2) must be paid on a cost-sharing basis of 50% by the employer and 50% by the employee. Except as provided in this section, contributions shall be made in the manner prescribed in section 42. An employee contribution for unfunded actuarial accrued liability must not be assessed to an employee based on any portion of an unfunded liability caused by the failure of an employer to make a required contribution. Following the determination of the cost-sharing basis under this subsection, section 41(2)(c) and (e) applies.

    (4) The contributions of a member for unfunded actuarial accrued liability must be treated as picked-up contributions under the internal revenue code, deducted by the employer, and remitted as employer contributions to the general fund of the retirement system and must only be used to finance unfunded actuarial accrued liabilities of the retirement system.

    (5) To the extent and upon approval by the Internal Revenue Service, the retirement system for the Tier 1 plan and the plan administrator for the Tier 2 plan may also determine the extent to which some or all of the individuals performing services for an entity not participating in the retirement system that receives any funding from the state school aid fund established in section 11 of article IX of the state constitution of 1963 may participate in the Tier 1 and Tier 2 plans.