The annual event taking place Sunday in Selma commemorates the beating of voting rights marchers on "Bloody Sunday" in 1965 as they began a voting rights march from that city to Montgomery. The march prompted Congress to pass the Voting Rights Act, which opened Southern polling places to millions of African-Americans.
Jackson said efforts to diminish the effects of the act continue.
The U.S. Supreme Court heard a challenge Wednesday to a key part of the Voting Rights Act.
Jackson said the South will see more gerrymandering and more at-large elections if the Supreme Court throws out a requirement for the Justice Department to review election law changes in states with a history of discrimination.