(COURIER-JOURNAL) -- The Kentucky Supreme Court struck down Louisville's minimum wage law in a 6-1 decision Thursday morning, which could cut the salaries for thousands of low-paid workers.

In an 11-page ruling written by Justice Bill Cunningham, the high court said Metro Council exceeded its authority when it voted to boost hourly salaries to $9 an hour nearly two years ago. The justices said requiring local businesses to pay workers a higher wage conflicts with state law.

"In other words, what the statute makes legal, the ordinance makes illegal and, thus, prohibits what the statute expressly permits," Cunningham said. "Therefore, the ordinance is invalid unless additional statutory authority permits municipalities to raise the minimum wage."

The decision overturns an earlier ruling by Jefferson Circuit Court which upheld the ordinance. Cunninghan was joined in the opinion by five other justices. Justice Samuel T. Wright III dissented.

Cunningham said Kentucky's minimum wage law is part of a "comprehensive statutory scheme" on wage and hour laws established by the legislature for the entire state. The statute itself contains no room for local legislation, he said.

In July, Louisville's lowest-paid workers got a pay raise that lifted their salaries to $8.25 an hour. It was the second of three pay hikes that council Democrats spearheaded two years ago.

The ruling is a body blow for council Democrats, labor unions and others who said cities needed to take the lead on addressing the country's widening income gap. Some supporters said Thursday's ruling means tens of thousands of workers who were set to receive pay increases must pressure state lawmakers to act.

"It is now up to the General Assembly to take action when they next meet to correct this injustice and ensure more Kentuckians who work can meet their basic needs," Jason Bailey, executive director of the Kentucky Center for Economic Policy, said in a statement.