Why did John Lochner's lawyers argue that the Bakeshop Act was class legislation?

In the case of Lochner v. New York, lawyers for John Lochner argued that the Bakeshop Act constituted prohibited class legislation because the law was applied inconsistently. Specifically, they contended that the statute unfairly targeted certain bakers while exempting others, such as those employed in hotels, restaurants, and clubs.1

By challenging the law as class legislation, Lochner’s legal team sought to demonstrate that the regulation did not fall within the state's legitimate police power, which is the authority to enact laws for the protection of public health, safety, and welfare. They argued that because baking was not an inherently dangerous or unhealthful trade—unlike industries such as mining—the state lacked the justification to impose special regulations on it. They further warned that if the court permitted this law to stand, it could set a precedent allowing the government to eventually regulate all trades under the guise of police power.1