The ruling is a major victory for Republican Senate candidate David McCormick, who holds a very narrow lead over Democratic Sen. Bob Casey ahead of a statewide recount.

Pennsylvania’s state Supreme Court is weighing in on a flashpoint amid ongoing vote counting in the U.S. Senate election between Democratic Sen. Bob Casey and Republican David McCormick

The recount underway in Pennsylvania’s U.S. Senate race marks the end of a chaotic post-election period that has become the latest example of how disputed election rules can expose weak points in a core function of American democracy.

The Pennsylvania Supreme Court on Monday ordered election officials in the state to stop counting mail-in ballots marked with the wrong date or missing a date from their outer envelope.

Pennsylvania's high court ordered state county election officials on Monday to not count "invalid" mail-in ballots in the U.S. Senate race between Democratic Sen. Bob Casey and his Republican challenger,