In a unanimous ruling, the judges said there was no discriminatory intent behind the law, ruling that it would not diminish African-Americans’ voting rights because people who face a “reasonable impediment” to getting an acceptable photo ID can still vote if they sign an affidavit.

The judge declined to let the law take effect immediately, “given the short time left before the 2012 elections and given the numerous steps necessary to properly implement the law … and ensure that the law would not have discriminatory” effects.

South Carolina voters who now lack the proper photo ID are disproportionately African-American, so proper and smooth functioning of the law “would be vital to avoid unlawfully racially discriminatory effects,” according to the decision, written by Judge Brett M. Kavanaugh of the U.S. Court of Appeals for the District of Columbia Circuit. “There is too much of a risk to African-American voters for us to roll the dice,” he said.

South Carolina is one of 16 states, mostly in the South, where election laws are subject to Justice Department approval under the federal Voting Rights Act because of a history of discrimination. South Carolina’s was the first law to be refused federal OK in nearly 20 years, which led state officials to challenge that decision in federal court.

The state’s Republican-controlled Legislature pushed the law through last year despite heavy opposition from African-American lawmakers. GOP Gov. Nikki Haley signed it last December.

Voter ID laws and other restrictions on voting became priority issues in mostly Republican legislatures and for governors after the 2008 elections. Opponents have described them as responses to the record turnouts of minorities and other Democratic-leaning constituencies that helped put Barack Obama, the first African-American president, in the White House.

Such laws have become a critical issue in this year’s election because of the tight presidential race between Obama and Republican nominee Mitt Romney. Supporters have pitched these laws as necessary to deter voter fraud, although very few cases of impersonation have been found.

Officials from South Carolina could not cite a single case of such fraud during the trial, but they said the law would help enhance public confidence in the election system and prevent other types of fraud.

South Carolina’s law requires voters to show a driver’s license or other photo identification issued by the state Department of Motor Vehicles, or a passport, military photo identification or a voter registration card with a photo.

The other judges in the case were Colleen Kollar-Kotelly and John D. Bates of the U.S. District Court in Washington.

Kollar-Kotelly was appointed by President Bill Clinton. Bates and Kavanaugh were appointed by President George W. Bush.

The case number is 2012-203.