An SEC registrant must file a Form 8-K when its external auditor resigns, declines to stand for reelection, or is dismissed.
SEC registrant should file form 8k when external auditor is dismissed 
mnli hypothesis: SEC registrant should file form 8k when external auditor is dismissed  premise: An SEC registrant must file a Form 8-K when its external auditor resigns, declines to stand for reelection, or is dismissed.