KANSAS CITY, Mo. (AP) — Kansas City’s minimum wage would rise to $13 an hour over about four and a half years under a newly approved ordinance.

The city council voted Thursday to approve the measure. The proposal has the backing of low-wage workers, but business groups are questioning its legality. It calls for businesses with more than 15 employees to begin paying at least $8.50 an hour on August 24th. The current state minimum is $7.65.

The minimum wage would rise again on January 1st, 2017, to $9.82 an hour, and be followed by annual increases until it hits $13 an hour in 2020. Cost-of-living adjustments would be made in subsequent years.

Workers who are 17 or younger are among those who would be exempted.