The U.S. Supreme Court dealt a resounding blow to the so-called “personhood” movement this week, when it declined to hear an appeal for a proposed ballot initiative that -- if passed -- would effectively outlaw abortion in Oklahoma.

The initiative, proposed by Personhood Oklahoma, would seek to add an amendment to the Oklahoma state constitution that says fertilized eggs are human beings and, as a result, are entitled to the same constitutional protections. Oklahoma Attorney General Scott Pruitt had approved the ballot title and summary and Personhood Oklahoma was in the process of collecting the signatures needed to place the issue on the ballot, when the American Civil Liberties Union and the Center for Reproductive Rights filed a lawsuit to keep the issue from appearing before voters.

“Today’s rejection by the highest court in the nation is yet another resounding message to opponents of reproductive freedom that such extremist assaults on our fundamental rights will not stand,” Nancy Northup, the president and CEO of the Center for Reproductive Rights, said Monday.

In April, the Oklahoma Supreme Court called the proposal “clearly unconstitutional” under the U.S. Supreme Court’s 1992 decision upholding abortion rights in Planned Parenthood v. Casey. Opponents argue that by conferring rights on an embryo, the initiative could ban abortion, in addition to many forms of hormonal contraception and in vitro fertilization.

Although CBS News reports Personhood Oklahoma co-founder Dan Skerbitz said the group “will not rest until our voices are heard, and our women and children are protected from abortion,” the personhood movement has – so far—been largely unsuccessful.

In Oklahoma alone, a personhood bill passed in the state Senate during this year’s legislative session was ultimately not heard by the House of Representatives. In Nevada and Florida, supporters failed to collect enough signatures to land personhood amendments on the ballot, while previous proposals in Colorado and Mississippi were rejected by a popular vote.

But the U.S. Supreme Court’s refusal to even consider the issue indicates the personhood effort is something even conservative leaders may want to keep their distance from. Only four of the nine justices need to agree for the court take on a case. Considering the fact that the court currently has exactly four conservative justices, their rejection could be a sign that they are unwilling to wade into a case that could have such far-reaching consequences for abortion rights.