§ 163-a. Supplementary plan. 1. For the purposes of this section, the term "supplementary plan" shall mean a health benefit plan which provides an adjustment to the deductible or co-insurance liability or to the benefits provided by the statewide health benefit plan purchased pursuant to section one hundred sixty-two of this article.

2. The president may require the insurer of a supplementary plan to the statewide health benefit plan, provided as a result of a collectively negotiated agreement pursuant to article fourteen of this chapter, to make a comparable supplementary plan available to participating employers as of the implementation date of the state employees' supplementary plan. The comparable supplementary plan shall be experience rated as to those participating employers electing it, with the costs thereof allocated equitably among them.

3. Every participating employer which, on or before July first, nineteen hundred eighty-five, entered into a collectively negotiated agreement pursuant to article fourteen of this chapter with employee organizations representing its employees to provide the statewide health benefit plan shall provide such comparable supplementary plan on the date established by the president until the expiration of such negotiated agreement.