Supreme Court Justice Anthony Kennedy’s retirement could pave the way for major changes in women’s health and abortion issues, possibly some of the biggest since the 1973 landmark case Roe v. Wade, if the Senate confirms a conservative justice.

Kennedy has been a key swing vote on women’s health issues. Two years ago, he joined the plurality in Whole Woman’s Health v. Hellerstedt, a major abortion rights case, which struck down a Texas law that would have resulted in the closure of most of the state’s abortion clinics.

In 1992, in Planned Parenthood v. Casey, he joined the plurality in reaffirming the Roe decision while allowing states to regulate the procedure unless it imposes an “undue burden” on women’s right to access abortion. The decision differed from Roe by allowing state regulation on abortions to take place in the first trimester.

This week, Kennedy sided with the conservative justices in National Institute of Family and Life Advocates v. Becerra, a free speech case challenging a California state law. It required licensed crisis pregnancy centers to post notices explaining that the state offers subsidized family planning services, including abortion, and required unlicensed centers to disclose that they do not have medical personnel on staff. The opinion said the pregnancy centers “are likely to succeed” in a constitutional challenge to the restrictions involving licensed centers.

Overturning Roe v. Wade, which guarantees a woman’s legal right to abortion, has been a goal of many anti-abortion groups since the ruling was issued. Momentum picked up after President Donald Trump, backed by a Republican-controlled Congress, was elected.