ST. LOUIS — Both of Missouri’s urban mayors are among supporters of an effort to let voters decide if Missouri’s minimum wage should rise to $12 an hour by 2023.

St. Louis Mayor Lyda Krewson and Kansas City Mayor Sly James said Monday that they support the “Raise Up Missouri” ballot initiative. Organizers need 100,000 signatures by May.

The petition drive is in response to Missouri’s minimum wage law that took effect Monday. It prohibits local government from a minimum wage higher than Missouri’s statewide wage of $7.70 per hour. A $10 wage in St. Louis and a similar wage approved by Kansas City voters this month are nullified.

“Today is a sad day for workers,” Krewson said at a rally Monday.

The ballot measure would increase the statewide minimum wage to $8.60 per hour in 2019, with 85-cent raises each year after that until 2023. Other supporters include Columbia Mayor Brian Treece and St. Louis County Executive Steve Stenger.

Republican Gov. Eric Greitens, who allowed the minimum wage measure to become law without his signature, declined comment Monday but has said previously that the higher wage in St. Louis forces small businesses to either cut hours or cut jobs. He cited a University of Washington study suggesting Seattle’s $15 minimum wage cost workers hours on the job, resulting in an average loss of $125 per month.

Another study by the University of California at Berkeley had a different result, finding that the Seattle wage hike boosted pay for restaurant workers without costing jobs.

St. Louis aldermen approved the $10 minimum wage in 2015. A two-year court battle ended in May when the Missouri Supreme Court ruled in favor of the city. Within days of that ruling, the Republican-led Legislature passed the new law.

A campaign was launched in July to pressure St. Louis businesses to keep the $10 minimum wage. Organizers said more than 150 businesses signed an online petition agreeing to do so. But workers at some fast-food restaurants were told to expect pay reductions once the new law took effect.

The Kansas City Council on Aug. 17 adopted a resolution encouraging employers to voluntarily comply with the higher wage approved by voters. It wasn’t clear how many did so.

At least two other states have recently passed so-called “pre-emption laws” knocking down higher wages established by local governments.

Alabama’s law nullified a 2015 Birmingham ordinance that would have raised the city minimum wage to $10.10 by July 2017. Former Iowa Republican Gov. Terry Branstad in March signed a law negating wage hikes in two counties and stopping a third before it could take effect. The statewide minimum wage in Alabama and Iowa is $7.25 per hour, the U.S. minimum.

Twenty-nine states and the District of Columbia have minimum wage rates above the U.S. minimum, according to the Economic Policy Institute.