The US Supreme Court on Monday declined an invitation to examine whether the Oklahoma Supreme Court acted correctly when it struck down a proposed “personhood” amendment that sought to grant state constitutional protections to human embryos starting at conception.

The justices turned aside the appeal in a one-line order without comment. The case was Personhood Oklahoma v. Barber (12-145).

The appeal stemmed from an April 30, 2012, ruling by the Oklahoma Supreme Court, which invalidated a proposed statewide ballot initiative that aimed to define a fertilized egg as a person with full rights to due process and equal treatment.

The personhood measure sought to establish that the fertilized egg/person could not be denied equal protection because of age, place of residence, or medical condition.

Opponents attacked the ballot initiative as an attempt to ban abortion in Oklahoma in violation of US Supreme Court precedents upholding the constitutionality of the procedure.

They said the amendment, if adopted, would confer rights on a fertilized egg that would trump the rights of women to decide whether and when to conceive and whether to carry a pregnancy to term.

Lawyers representing the opponents argued that in addition to banning abortion, the amendment would block use of many forms of contraception and in vitro fertilization.

The Oklahoma high court agreed with the opponents, ruling the ballot question “void on its face.”

The court said the proposed measure was “clearly unconstitutional” under the US Supreme Court’s 1992 decision upholding abortion rights under the US Constitution in Planned Parenthood v. Casey.

Antiabortion supporters of the personhood initiative challenged the Oklahoma Supreme Court’s decision, saying that the court should have allowed the measure – and the political process surrounding it – to move forward to a statewide vote before confronting the hypothetical question of whether an enacted amendment would clash in every respect with the US Constitution.

“It would appear that no further discussion or vote will be allowed if opponents can raise one hypothetical application that would conflict with federal law if the proposed amendment were passed,” wrote Mathew Staver, a lawyer for the personhood initiative, in a brief urging the Supreme Court to take up the case.

Mr. Staver contrasted the Oklahoma decision with a similar legal battle over a 1994 abortion amendment in Wyoming.

“In stark contrast to the Oklahoma Supreme Court’s ruling, the Wyoming Supreme Court reached precisely the opposite conclusion in a case proposing a direct ban on abortion, and allowing the matter to proceed to the ballot,” he said.

The Wyoming Human Life Protection Act banned abortion in the state except in cases of rape or incest, or to save the life of the mother. The Wyoming court ruled the proposed law would directly contravene US Supreme Court abortion precedents. But the judges concluded that part of the proposed measure (a prohibition on state funding of abortion) would be constitutional.

“The court concluded that despite the fact that a portion of the act was unconstitutional, it should be placed on the ballot and the people given an opportunity to vote on it,” Staver wrote.

In the Oklahoma case, Staver said that the people of Oklahoma reserve to themselves the power to amend the state constitution and that state judges violate the constitutional principle of separation of powers when they seek to short-cut that process.

State courts in Mississippi and Colorado have allowed personhood initiatives on the ballot. Voters in both states rejected the proposals.

The Oklahoma Supreme Court said in its decision that its precedents require that the court strike down proposed constitutional amendments that are “repugnant to the Constitution of the United States.”

“The United States Supreme Court has spoken on this issue,” the unanimous Oklahoma court declared. “The measure is clearly unconstitutional pursuant to Planned Parenthood v. Casey. The states are duty bound to follow its interpretation of the law," the court said.

“The mandate of Casey is as binding on this court today as it was twenty years ago,” the Oklahoma judges said.