Once again, a referendum asking Ohio voters to legalize casino gambling will appear on the November ballot. Ohio Secretary of State Jennifer Brunner certified the referendum on Tuesday, saying that a committee backed by gambling interests had collected more than 450,000 valid signatures. The referendum will ask voters whether a casino should be allowed in each of the state's four largest metropolitan areas: Cincinnati, Cleveland, Columbus, and Toledo. Last week, the Ohio legislature approved a budget that will allow up to 2,500 slot machines at each of Ohio's seven racetracks. That measure is expected to be challenged in court by several anti-gambling groups that have contended that the legislature does not have the constitutional authority to authorize slot-machine gambling. Ohio voters have defeated four separate ballot issues on expanded gambling since 1990. The latest was last November, when voters rejected the approval of a single casino in southern Ohio.