Justice Clarence Thomas said Tuesday the Supreme Court will not be able to duck the issue of abortion forever and raised concerns about the potential for abortion to “become a tool of eugenic manipulation.”

Thomas’ warning came in a concurring opinion in which he agreed with a decision by the Supreme Court not to review a provision of an Indiana law that bans abortion on the basis of race, sex, or disability. In an unsigned opinion, the high court upheld another provision of the law that mandates the burial or cremation of fetal remains after an abortion.

The measures at the center of the dispute were signed in 2016 by then-Gov. Mike Pence.

Thomas wrote that “further percolation may assist” the court’s review of the abortion restrictions but argued the Indiana law and others like it “promote a state’s compelling interest in preventing abortion from becoming a tool of modern-day eugenics.”

“Although the court declines to wade into these issues today, we cannot avoid them forever,” Thomas wrote in his 20-page concurring opinion. “Having created the constitutional right to an abortion, this court is dutybound to address its scope.”

The conservative justice focused specifically on Indiana’s prohibition of abortion based on sex, race, or disability and charted the history of the eugenics movement in the United States.

The dispute before the court, he warned, “highlights the fact that abortion is an act rife with the potential for eugenic manipulation.”

“Enshrining a constitutional right to an abortion based solely on the race, sex, or disability of an unborn child, as Planned Parenthood advocates, would constitutionalize the views of the 20th-century eugenics movement,” Thomas wrote.

Thomas highlighted comments from Planned Parenthood founder Margaret Sanger and its former President Alan Guttmacher and cited a “growing body of evidence” that suggests “eugenic goals are already being realized through abortion.”

In Iceland, for example, Thomas wrote the abortion rate for children diagnosed with Down syndrome in utero is nearing 100%. He also noted that the nationwide abortion rate among black women in the U.S. is roughly 3.5 times that for white women.

“Some believe that the United States is already experiencing the eugenic effects of abortion,” Thomas said.

The Indiana case, which was discussed by the justices at more than a dozen of their private conferences, has been closely watched, as it could have provided an early test of abortion rights before the court’s new 5-4 conservative majority.

Several states have passed laws barring abortion after a fetal heartbeat is detected, while others have enacted measures designed to restrict the procedure. Such laws are designed to challenge Roe v. Wade, the 1973 Supreme Court decision that established a woman’s right to an abortion.

But Thomas warned the court’s past cases reaffirming the right to an abortion, namely the 1992 decision Planned Parenthood v. Casey, “did not decide whether the Constitution requires states to allow eugenic abortions.”

While the court’s opinion in the Indiana case was unsigned, Justices Ruth Bader Ginsburg and Sonia Sotomayor said they would have denied review of both provisions of the law at issue.

Thomas and Ginsburg sparred in the footnotes of their respective opinions. Ginsburg’s dissent, Thomas said, “makes little sense,” while Thomas’ criticism “displays more heat than light,” Ginsburg wrote.