Missouri Supreme Court judges heard arguments Wednesday over the constitutionality of a law passed in the wake of unrest in Ferguson that would cap traffic fines and court fees.

Legislators passed the law in an attempt to address concerns raised about law enforcement and court tactics after the fatal 2014 police shooting of Michael Brown in the St. Louis suburb. A U.S. Department of Justice report last March said Ferguson had a profit-driven municipal court system and a police force that frequently targeted blacks.

So Missouri lawmakers passed legislation capping the amount most cities can keep from traffic fines and court fees at 20 percent of their budgets, down from 30 percent.

St. Louis County municipalities face a lower 12.5 percent limit. Several other provisions of the law, including requirements for law enforcement accreditation and written policing policies, are also set to only take effect in St. Louis County.

Some heralded the law as a step toward municipal and police reform. But a dozen St. Louis County cities sued, arguing that it unfairly targets municipalities in that area. The Missouri Constitution has bans on many "special" laws, which are measures that single out specific areas and don't apply across the state.

Assistant Attorney General Andrew Hirth agreed when asked by Judge Zel Fischer whether legislators directed the law toward areas they considered problematic. In his argument, Hirth said there's "no question" St. Louis County is treated differently.

But he countered that the Supreme Court "has never held that the Legislature can't legislate by neighborhood."

"There are local problems in different parts of the state that require different remedies," Hirth said.

He said there are dozens of laws on the books that similarly single out areas based on population, adding that other counties could fall under the law depending on population growth or mergers. He also said the legislation doesn't fit that category because it impacts the dozens of municipalities within St. Louis County.

Philadelphia-based attorney David Pittinsky said based on current population trends, it could take at least 150 years before Jackson County, the next highest-population county in the state, to qualify. He said that makes the law narrowly tailored toward a certain area and described it as a "classic" special law.