A group with ties to the Michigan Chamber of Commerce is challenging a 2018 ballot initiative that aims to end political gerrymandering by empowering an independent commission to draw the state's congressional and legislative districts.

Citizens Protecting Michigan's Constitution filed a challenge Thursday with the state elections board, announcing that it had also sued in the state appeals court a day before. It contends ballot committee Voters Not Politicians is seeking to amend so many parts of the state constitution that a constitutional convention is required, and that the proposal does not list all of the sections of the constitution that would be abrogated.

The conservative Citizens Protecting Michigan's Constitution — which helped to defeat five ballot measures in 2012 — received $85,000 in in-kind legal services in March from the Michigan Chamber Litigation Center. The Michigan Chamber of Commerce, whose political action committee gave $100,000 in February, came out in opposition to the redistricting proposal and two other ballot initiatives last fall.

The state elections bureau recently released a sample pulled from 425,000 signatures submitted by the redistricting group. The deadline to challenge signatures was Thursday.

The ballot committee opposing the measure said the bipartisan Board of State Canvassers is not required to complete it canvass of signatures and certify the petitions until early September. It urged the board to take no further action until the appeals court rules on the legal challenge.

The all-volunteer Voters Not Politicians, which defied the odds by collecting hundreds of thousands of signatures without having to pay them, said it will vigorously respond to the "procedural objections" lodged by the opposition.

"Our proposal affects only one aspect of state government: redistricting. It does not interfere with or modify any other aspect of state government," said Jim Lancaster, an attorney for the anti-gerrymandering group.

Gerrymandering has led to seats that are drawn to guarantee as many comfortable districts as possible for the party in power. The majority party, which was the GOP after the 2010 and 2000 population counts, pads its advantage by translating its votes into a greater share of victories.

Under the proposal, a commission of citizens who meet certain qualifications would handle redistricting. There would be four Democrats, four Republicans and five members with no affiliation with either major party.

The panel would be prohibited from providing a "disproportionate advantage" to a political party, using "accepted measures of partisan fairness."