The nine justices ruled unanimously that Initiative Petition No. 395 is unconstitutional and cannot be placed on the November ballot, The Oklahoman of Tulsa, Okla. reported.
The ruling came in a Center for Reproductive Rights lawsuit that charged the personhood proposal would effectively ban all abortions and many types of birth control as well as threatening fertility treatments.
It was filed on behalf of Oklahoma physicians who provide a wide range of reproductive healthcare to women and women who would have been affected by the amendment.
Director Dan Skerbitz of Personhood Oklahoma said his group is studying options, including the possibility of getting lawmakers to pass a resolution to put the issue directly on the ballot.
Skerbitz said earlier that the purpose of seeking a constitutional amendment is to draw a legal challenge to the U.S. Supreme Court's 1973 Roe V. Wade ruling that recognized a woman's right to an abortion in some circumstances.