The minimum wage in St. Louis was rolled back on Monday from $10 an hour to $7.70, the statewide minimum, part of a broader trend of Republican state lawmakers pushing legislation that prevents local governments from setting their own labor law regulations.

Since the beginning of 2016, 15 states have passed 27 such local pre-emption laws, according a study released Monday by the liberal Economic Policy Institute, made possible by the GOP's strong advantage in statehouses across the country. Republicans control 33 governorships and 67 of the 98 partisan state legislative chambers. In 24 states, Republicans have complete control, holding both the governor's office and majorities in both state legislative chambers.

"Conservative state legislatures are now using pre-emption to eliminate the authority of a lower level of government to regulate a certain issue. In practice, these laws are being used to strip authority from local governments who seek to increase protections for workers; the laws do so by prohibiting these local governments from increasing their labor/employment standards above the state floor," said Marni von Wilpert, EPI's associate labor counsel.

Missouri follows Arkansas, Iowa, Ohio, North Carolina, Kentucky, Idaho, and Alabama in passing laws in the last two years that prohibit minimum wages above the state floor. Other states have passed laws prohibiting local government from enacting different rules for mandating paid leave or regulating work schedules, among other issues.

Republicans and business groups have argued that while states should be free to experiment with different laws, those laws should be uniform within the state itself. Having multiple rates in a state can be disruptive, argued Jeremy Cady, Missouri director of Americans for Prosperity, arguing that his state's lawmakers were right to roll back the law.

"St. Louis was the only place that put a higher minimum wage into effect, but Kansas City put it on the ballot earlier this month," Cady noted. The Kansas City ballot, which would have raised the city's rate to $15 an hour by 2022, was rendered moot by the rollback law passing.

Nevertheless, rolling back a minimum wage to a lower level is a tricky issue for lawmakers. After Missouri lawmakers passed the rollback legislation, Republican Gov. Eric Greitens didn't sign the law, but he didn't oppose it either.

"We have different wages across the state. It's created uncertainty for small businesses. And it all could have been avoided if the politicians had done their job on time. I disapprove of the way politicians handled this. That's why I won't be signing my name to their bill," Greitens said in a July statement.

Cady said the bottom line is that Republicans were able to undo the St. Louis and Kansas City ordinances. He was particularly relieved in the latter case. "Seattle is the prime example of what can go wrong there," he said, referring to economic reports showing that's city's $15-an-hour rate is harming low-income workers.