With the $37 billion deal between Aetna and Humana still under federal review, a state insurance department says it would block the merged company from selling certain plans if the deal is ultimately approved. The Missouri Department of Insurance issued a preliminary order Tuesday night saying the deal between Connecticut-based Aetna and Louisville’s Humana would reduce competition and harm some consumers in the state. The order would prevent the merged company – which would be the second-largest insurer in the country – from selling individual, small-group and group Medicare Advantage plans in Missouri. It would also block the company from selling individual Medicare Advantage plans in more than half of Missouri counties. Humana employs more than 12,500 people in Louisville. The Justice Department is reviewing the proposed merger, and the Missouri decision has no bearing on that outcome. Still, Missouri is the first state to officially disapprove of the deal. Aetna spokesman Rohan Hutchings said the company would try to persuade Missouri officials to reconsider. The state's preliminary order is the result of public hearings that took place earlier this month. “We are disappointed with the Missouri order but expect to have a constructive dialogue with the state to address their concerns," he said. Aetna and Humana have 30 days to appeal the decision. A spokesman for Humana did not return a request for comment. The Kentucky Department of Insurance approved the proposed merger in February without taking public input. Justice Department attorneys continue to review the Aetna-Humana merger and another proposed mega-deal between Anthem and Cigna. Taken together, the two deals include four of the nation's five-biggest health insurance companies. UnitedHealth Group is by far the largest single insurer, with a value of nearly $129 billion as of market close on Wednesday.