MILWAUKEE (CBS 58) -- A legal fight is cooking up over Milwaukee's newly approved food truck ordinance that will go into effect Saturday, May 9.

On Thursday, May 7, the Wisconsin Institute for Law and Liberty filed a lawsuit on behalf of a local food truck owner, calling the new rules "unconstitutional." The lawsuit is seeking an emergency stay of the law to stop it from going into effect. 

The ordinance, which was approved unanimously by the Milwaukee Common Council last month, requires food trucks operating downtown to shut down earlier under rules aimed at curbing late-night violence. 

But the lawsuit says food trucks shouldn't be the ones blamed for that violence, and the ordinance interferes with the food trucks owners' rights to earn a living. It also claims that the ordinance singles out food trucks specifically while allowing brick and mortar restaurants in the same areas to stay open. 

We are expecting to hear from officials who filed the lawsuit as well as from the food truck owner they are representing.

This is a developing story. Stick with CBS 58 on-air and online for updates.