OKLAHOMA CITY (AP) — Oklahoma's highest court on Tuesday rejected a legal effort to block a plan for a public vote on whether to expand Medicaid to tens of thousands of poor residents.

Just hours after hearing oral arguments in the case, the Oklahoma Supreme Court rejected the challenge spearheaded by a conservative think-tank that has long opposed to making the federally funded health insurance program available to more people.

The court's decision authorized supporters to proceed with gathering the nearly 178,000 signatures they will need to get the question on the ballot. The plan was chall...