Former President Bill Clinton speaks Wednesday during the Civil Rights Summit in Austin, Texas. The summit marks the 50th anniversary of the Civil Rights Act.

AUSTIN, Texas — Former President Bill Clinton used the 50th anniversary of the Civil Rights Act to criticize efforts in several states to restrict voting, notably photo identification requirements, saying they threaten to roll back half a century of progress.

Clinton spoke Wednesday night during the Civil Rights Summit at the Lyndon B. Johnson Presidential Library at the University of Texas in Austin. The library is hosting the three-day event to mark the anniversary of the landmark 1964 law that banned widespread discrimination against racial and ethnic minorities and women.

President Barack Obama is scheduled to give the keynote address today and former President George. W. Bush will wrap up the summit later today.

Clinton, the 42nd president, praised Johnson for pushing through laws that helped remove political and economic barriers for millions. He noted Johnson was a “son of the South” and a “a Texan bred with the state’s outsized ambitions (who) saw limitless possibilities in the lives of other people like him, who just happened to have a different color skin.”

He also praised those who gave their lives in the civil rights struggle, such as Martin Luther King, Medgar Evers and other victims of bombings and shootings.

Clinton spent much of his speech addressing last year’s U.S. Supreme Court ruling that struck down key provisions of the 1965 Voting Rights Act, which was also signed into law by Johnson. The ruling allows several states with a history of discriminatory voting laws, mostly in the south, to change election laws without federal approval.

“It sent a signal throughout the country,” Clinton said of the ruling. “We all know what this is about. This is a way of restricting a franchise after 50 years of expanding it ... Is this what Martin Luther King gave his life for?”