LANSING (AP) — The Michigan Republican Party sued Thursday to block the formation of a commission to draw congressional and legislative lines in 2021, saying the voter-approved change is unconstitutional because there will be no reliable way to verify the panel’s political makeup.

The lawsuit, the second filed by Republicans in less than a month, seeks an injunction against Democratic Secretary of State Jocelyn Benson, whose office is implementing the law. Others joining the newest challenge include GOP chairwoman Laura Cox, former Secretary of State Terri Lynn Land and state Rep. Hank Vaupel.

The 2018 constitutional amendment requires that a randomly selected commission of four self-identified Democrats, four self-identified Republicans and five unaffiliated members draw political districts instead of the Legislature, starting in 2021. It is a bid to curtail gerrymandering in a state where the GOP has had one of the largest partisan legislative advantages in the country after controlling the once-a-decade process in 2011.

The suit alleges that the law “can, and likely will, result in a situation where those who do not represent (the party’s) interests are selected as Republican commissioners and, by implication, standard bearers of the political party.” It says that other states with an independent redistricting panel are different because they have party registration or the political parties are involved in determining their representatives on the commission.

Those excluded from serving on Michigan’s panel include people who currently are or have in the previous six years been elected partisan officials or candidates, their paid consultants or employees, legislative workers, lobbyists and their employees, or political appointees not subject to civil service classification. Also barred from the paid positions are those individuals’ parents, children and spouses.