In the lochner v. new york case of 1905, the supreme court ruled that states could not

a) pass labor laws to protect women.
b) increase protections for children.
c) pass laws concerning workplace safety.
d) regulate working hours.

The correct answer is D.

Lochner v. New York ( 1905 ), was a landmark U.S. labor law case that held that settings maximum working hours for bakers was unconditional and violated the 14th Amendment.

The Court held that the Constitution prohibits states from  interfering with most employment contacts because the right to buy and sell labor is a fundamental freedom protected by the 14th Amendment.

In the Bakeshop Act of 1897, the state of New York passed the so called 'labor law' that prohibited employees in bakeries to work more than 60 hours in a week. Joseph Lochner, a bakery owner, was fined 50$ for allowing an employee to work more hours than the allowed 60. Lochner appeared to the U.S. Supreme Court.

The Supreme Court construed that the 'labor law' was an interference with 'the right of contract between the employer and the employees' and that each individual had the right 'to make a contract in relation to his business as part of  the liberty of the individual'.  The due process clause in the 14th Amendment prohibits states from depriving any person of life, liberty or property without the due process of the law.

The Lochner v. New York case was overruled in 1937 in West Coast Hotel v. Parrish.