Washington (CNN) Justice Clarence Thomas took an unusual foray in an abortion related court opinion on Tuesday, warning his colleagues of the potential that abortion could become a "tool of eugenic manipulation."

Diving deep into the controversial movement from the early 20th century, aimed at improving society by encouraging the reproduction of certain traits, Thomas also charged that Planned Parenthood founder Margaret Sanger was once "particularly open about the fact that birth control could be used" for eugenic purposes.

Why eugenics? At the core, Thomas was explaining his thinking about an Indiana abortion law that bans abortion motivated solely by the race, sex or disability of the fetus. But critics say he was also taking up an oft-used argument made by opponents of abortion who say the procedure threatens those deemed undesirable by society.

"We denounce eugenics in all forms for the same reason we are working to fight abortion bans across the country," said Melanie Newman, senior vice president of communications and culture for Planned Parenthood Federation of America. "Every person should have the freedom to make their own decisions about their body."

The opinion came on Tuesday, when the court said it would leave in place a lower court opinion that invalidated a provision in Indiana's law.

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