(Reuters) - Ohio lawmakers approved redistricting reform on Tuesday aimed at curbing gerrymandering by changing how electoral district boundaries are drawn to ensure they do not favor one political party over another.

FILE PHOTO: Voters cast their votes during the U.S. presidential election in Medina, Ohio, U.S. November 8, 2016. REUTERS/Aaron Josefczyk/File Photo

The measure will be sent to voters in May.

Ohio House Speaker Pro Tempore Kirk Schuring said in a statement that the measure would create a fair and competitive system.

At least four states including Ohio, Michigan, Missouri and South Dakota are expected to put redistricting initiatives on ballots this year to curtail partisan gerrymandering, the manipulation of the composition of legislative districts to amplify the voting power of one party at the expense of another.

The issue is also playing out in courts. The U.S. Supreme Court on Monday refused to block a lower court ruling requiring Republican-drawn congressional districts in Pennsylvania to be redrawn immediately.

The Supreme Court is expected to rule later this year on whether Wisconsin Republican lawmakers created unconstitutional state legislative districts.

Ohio’s measure was a compromise reached by Republicans, Democrats and a voter advocacy group. When the legislature draws new maps, they must win three-fifths support from each chamber, including at least 50 percent support from the minority party.

A bipartisan commission would take over the process in case the two parties cannot reach that level of agreement.

Such commissions often ensure that more balanced maps are produced, said Michael Li, a redistricting expert at New York University’s Brennan Center for Justice.

In all, 24 U.S. states allow citizens to propose a law or constitutional amendment either to the legislature or directly to voters, according to the Brennan Center.

“Congressional redistricting reform will change the future of Ohio politics and has the potential to change our government in Washington, too,” Ohio Secretary of State Jon Husted said in a statement on Tuesday.

Driven largely by citizen groups, the measures, along with movements in other states to get such initiatives on ballots, come ahead of the 2020 Census.

Data from the census would be used in 2021 by state legislatures to redraw district voting maps, which are updated every 10 years, Li said.