SAN FRANCISCO — A federal judge has breathed new life into a class action lawsuit claiming that AT&T Mobility misled consumers by marketing certain data plans as “unlimited” while at the same time slowing the data speeds for consumers who crossed certain use thresholds.

U.S. District Judge Edward Chen of the Northern District of California, who had previously routed the suit to arbitration, on Wednesday granted the plaintiffs’ motion for reconsideration, agreeing that AT&T’s arbitration clause is now unenforceable under a California Supreme Court ruling that was handed down while his earlier ruling was pending on appeal.