According to the IRS instructions under the heading, "who can take this credit", it says, "you may be able to take this credit if you, or your spouse if filing jointly, made:
a) contributions (other than rollover contributions) to a Traditional or Roth IRA (including a myRA)
b) elective deferrals to a 401(k), 403(b), governmental 457(b), SEP, or SIMPLE plan
c) voluntary employee contributions to a qualified retirement plan as defined in section 4974(c) (including the federal thrift savings plan)
d) contributions to a 501(c)(18)(D) plan" https://www.irs.gov/pub/irs-pdf/f8880.pdf
If the mandatory state employees retirement contribution is the only plan that you contributed to, it would have to meet the above requirements. From the information that you are providing, it doesnt sound like it does. However, on page 48 of Pub 590A under the heading, "eligible contributions", it states, "For purposes of this credit, an employee contribution will be voluntary as long as it is not required as a condition of employment".
If you made contributions to other types of retirement plans for 2016, then they have to meet the IRS requirements listed above in order to be considered eligible contributions for this credit.
Please refer to pages 47-48 of Pub 590A under the heading, "retirement savings contributions credit", to review the requirements for claiming this credit.
https://www.irs.gov/pub/irs-pdf/p590a.pdf
