The dispute pits the plaintiffs against Republican Gov. John Kasich, The Columbus Dispatch reported. Kasich, unable to get the legislature to agree on Medicaid, turned to the board, which approved the expansion Monday in a 5-2 bipartisan vote.
The expansion would add 275,000 people to Medicaid rolls in Ohio, the 25th state to approve the expansion. The Affordable Healthcare Act, known as Obamacare, allows states to add residents with incomes as high as 138 percent of the federal poverty level to Medicaid.
Under the law, the federal government will pay 100 percent of the added cost for three years followed by 90 percent for an additional four years.
Many of those in the standing-room only hearing or gathered outside cheered the board's move Monday.
"This is the day we've been waiting for and working to for a long time," Gayle Channing Tenenbaum of the Public Children Services Association of Ohio told the Dispatch.
Ohio Right to Life supported Kasich. But the chapters in Cleveland and Cincinnati joined the lawsuit.
The lawsuit, filed with the state Supreme Court, says the move violates the Ohio constitution.
After Monday's vote, Senate Republicans said they would introduce a tax cut to be funded by money from hospitals that will receive more federal funding with the Medicaid expansion.