(KTRS) – A plan to increase the minimum wage in the city of St. Louis is facing a lawsuit.

The lawsuit was filed by the Missouri Chamber of Commerce, the Restaurant and Retailers associations, and other groups. The minimum wage hike calls for the bottom wage to be increased to $9 an hour in January of next year, with it increasing a dollar per year until it hits $11 in 2018.

The business groups argue that the wage increase causes “immediate and irreparable harm” by forcing them to comply with different wage rules in different municipalities.

A spokesperson for Mayor Francis Slay’s office says they anticipated the challenge and are prepared to defend the minimum wage increase.