RICHMOND, Va. (AP) — Virginia’s attorney general, who has vowed to go to court if needed to see the Equal Rights Amendment adopted, plans to announce “landmark civil rights litigation” dealing with the proposed Constitutional amendment, his office announced Wednesday.

Attorney General Mark Herring is partnering on the lawsuit with fellow Democratic attorneys general Kwame Raoul of Illinois and Aaron Ford of Nevada, Herring’s office said in a news release, which did not provide additional details about the litigation. A news conference to discuss it was planned for Thursday.

The announcement came two days after Virginia became the critical 38th state to ratify the measure, which would prohibit discrimination based on sex. Nevada and Illinois were the next-most recent states to ratify the ERA – Nevada in 2017 and Illinois in 2018.

Typically, constitutional amendments must be ratified by three-quarters of the states, or 38. But the ERA’s future is uncertain, in part because of a 1982 deadline for ratification that Congress enacted decades ago. Many legal observers expect its future to be determined in the courts.

Herring said on Monday that he was committed “to making sure that we use every single tool at our disposal to make sure the Equal Rights Amendment becomes a part of the United States constitution as it should be.”

On Tuesday, the National Archives and Records Administration confirmed it had received Virginia’s ratification documentation but said the archivist would “take no action to certify the adoption of the Equal Rights Amendment.”

A spokeswoman for Herring declined further comment on the litigation before it is filed.

The administration said it was following the advice of the Department of Justice’s Office of Legal Counsel, which issued a memo earlier this month saying that because the 1982 deadline has passed, it is too late for states to ratify the ERA. The only option for supporters now is to begin the ratification process all over again in Congress, the department said.

The National Archives said it would abide by that opinion “unless otherwise directed by a final court order.”

ERA advocates have vowed to fight to see the measure certified, either in court or in Congress, where there is a push to remove the deadline. Some ERA supporters argue that because the deadline was included in a preamble of the amendment, it is not legally binding.