Missouri Gov. Mike Parson on Friday vetoed a bill that would have allowed some motorcycle riders to drive without helmets, citing opposition to an unrelated provision in the measure.

The legislation would have repealed Missouri's helmet requirement for motorcycle riders who are at least 18 years old and have health insurance.

In a letter to lawmakers , Parson wrote that he vetoed the wide-ranging bill because of an unrelated section that dealt with suspending driver's licenses because of failure to pay court fines.

Parson wrote that the legislation would "significantly undermine" another law enacted after protests in Ferguson broke out following black 18-year-old Michael Brown's fatal shooting by a white police officer.

Brown's shooting didn't involve a traffic stop, but his death and the sometimes violent protests that followed drew attention to concerns about the mostly white police force's treatment of the predominantly black residents of the St. Louis suburb, including the use of traffic fines and court fees to boost revenue.

Parson said the legislation also likely violates the Missouri Constitution's ban on legislation that unfairly targets one city or region.

Missouri lawmakers have long tried to repeal the state's helmet requirement. The last time they succeeded was in 2009, but it was also vetoed by then-Gov. Jay Nixon.