By Steve Olafson
OKLAHOMA CITY (Reuters) - The Oklahoma Supreme Court on Monday struck down a ballot initiative that sought voter approval of a so-called "personhood" amendment to the state constitution to define an embryo as a human being from the moment of conception.
The ballot question would have asked Oklahoma voters to expand the definition of a human being to include a fertilized egg. But the state's highest court said the proposed constitutional amendment was "void on its face" because the U.S. Supreme Court already has decided the issue.
Passage of a personhood law or constitutional amendment would have the effect of banning abortion in the state, both supporters and critics have said.
"The measure is clearly unconstitutional," the court said in its decision.
The ruling marked the second major defeat in Oklahoma this year for the personhood movement, which wants full legal rights accorded to human embryos from the moment of conception.
A personhood bill passed the Oklahoma state Senate in February but the state's House of Representatives refused to bring it to a vote last week.
The petition was challenged in court last month by the Center for Reproductive Rights, the American Civil Liberties Union and local abortion rights groups.
"This amendment would have run roughshod over the fundamental, constitutionally protected reproductive rights of all Oklahoma women," said Nancy Northrup, president and chief executive of the Center for Reproductive Rights.
Supporters of the personhood drive were trying to gather 155,000 signatures of registered voters within 90 days to place the amendment on the November election ballot. No one from the Tulsa-based organization immediately responded to a request for comment.
Similar initiatives were successful in placing personhood questions on the ballot in Colorado and Mississippi, but voters in those states defeated the amendments.
(Editing by Greg McCune and Vicki Allen)