Conservative Supreme Court justices on Wednesday signaled strong doubts about the ongoing validity of a key part of the Voting Rights Act, passed in 1965 to end a century of attempts by formerly slaveholding Southern states to block blacks from voting.

During a tense and sometimes fractious oral argument, which extended beyond the scheduled hour, the nine justices considered the claim made by officials from Alabama's Shelby County that Section 5 of the Voting Rights Act was no longer needed nearly five decades later. The county in the Deep South state had long chafed at federal oversight.

Throughout the argument, conservative and liberal justices alike asked probing, tough questions of all parties, regularly interrupting the lawyers and speaking over one another.