California on Wednesday was hit with a lawsuit in federal court over its first-in-the-nation law requiring publicly traded companies to have women on their boards of directors, marking the second legal challenge to the measure.

The Pacific Legal Foundation, which filed the most recent suit, argued in the filing that the law — which, by 2021, will require boards with five members to have two women and boards with six or more members to have three women — violates the U.S. Constitution’s Equal Protection Clause, The Associated Press reported.

The group, which named California Secretary of State Alex Padilla (D), is also seeking to block the law from taking effect in other states where the proposal has been introduced, including Illinois, Massachusetts, New Jersey and Washington.

“The law mandates exactly what the equal protection clause forbids — taking into account things like sex or race,” Anastasia Boden, the foundation’s attorney, told the AP. “The Constitution is meant to ensure that people are free to be individuals. Here, the law assumes that people of the same sex are essentially interchangeable.”

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Boden added that corporations are putting more women on their boards anyway, making the law unnecessary.

“We are actually near boardroom parity,” Boden told the outlet. “We don’t need this law, which will actually cast doubt on the reason behind future hires.”

In September 2018, California became the first U.S. state to enact such a requirement, with then-Gov. Jerry Brown (D) declaring he signed the bill because “it’s high time that corporate boards” include women. At the time, Brown noted that there were “numerous objections” to the measure and that “serious legal concerns” had been raised about its implications.

When the bill was initially introduced, one-quarter of the state’s publicly traded corporations didn’t have any women on their boards. According to the measure, companies who fail to adhere to the requirements or do not report their board compositions to Padilla’s office can face more than $100,000 in fines.

In August, the conservative group Judicial Watch sued over the law, arguing that taxpayer money to enforce the measure would violate the state constitution. Padilla is also named in the lawsuit.