Kansas City must put a proposed minimum wage increase before city voters, the Missouri Supreme Court ruled Tuesday, leaving open the possibility that the plan could be challenged in court again.

The court unanimously reversed a Jackson County Circuit Court ruling from September that said a state law prohibited the city from adopting a minimum wage different from the state's minimum wage, which is $7.70 an hour. The high court ordered the city to take "all steps necessary" to put the proposal on the ballot.

A group of civil rights and social justice organizations had gathered signatures in 2015 to seek a public vote to raise the minimum wage to $15 an hour by 2020.

The group, which had aimed to have the issue on the November 2015 ballot, appealed the Jackson County Court ruling, arguing that the state law was unconstitutional.

In its ruling Tuesday, the Supreme Court said legal challenges to the minimum wage proposal can be challenged in court only if voters approve it.

"Challenges as to whether that ordinance – if approved by voters – would be invalid under (state law), as well as constitutional challenges to the validity (of state law) itself, remain hypothetical unless and until the voters have adopted the measure," the court said in its opinion. "Then, but only then, may courts entertain such challenges."

Kansas City spokesman Chris Hernandez said the city's law department is "currently reviewing the ruling and will soon advise the city council on possible next steps."