(Reuters) - A federal judge in Wisconsin ruled as unconstitutional on Friday a state law requiring any doctor performing an abortion to have privileges to admit patients to a nearby hospital.

U.S. District Judge William Conley temporarily blocked the law in August 2013, which requires doctors to have admitting privileges at a hospital located within 30 miles (50 km) of his or her practice, shortly after Republican Governor Scott Walker signed it into law.

Planned Parenthood of Wisconsin and Affiliated Medical Services, the state's two abortion providers, challenged the measure in court, saying it could force abortion clinics in Appleton and Milwaukee to close.

On Friday, Conley ordered a permanent injunction against the law, saying in his 91-page order and opinion that the law violated women's 14th amendment rights under the U.S. Constitution.

"The marginal benefit to women's health of requiring hospital admitting privileges, if any, is substantially outweighed by the burden this requirement will have on women's health outcomes due to restricted access to abortions in Wisconsin," Conley wrote.

"While the court agrees with the State that sometimes it is necessary to reduce access to insure safety, this is decidedly not one of those instances," he said.

Walker's office could not be reached immediately for comment on Friday night.

Last June, the U.S. Supreme Court decided against intervening in the case, turning away the state's appeal against a 7th U.S. Circuit Court of Appeals ruling that upheld Conley's earlier decision to temporarily block the law.

"We all want to protect patient safety - this law doesn’t do that," Planned Parenthood of Wisconsin CEO Teri Huyck said in a statement.

"Politicians passed this law in order to make it extremely difficult for women in Wisconsin to get safe and legal abortions, plain and simple," Huyck said.

The Guttmacher Institute, a research group supporting the right to abortion whose reports are cited by both sides in the debate, says that 14 states mandate abortion providers to be affiliated with a local hospital in some way.

(Reporting by Curtis Skinner in San Francisco; Editing by Paul Tait)