From Longman Dictionary of Contemporary Englishprior warning/noticeprior warning/noticeBEFOREa warning or announcement made before something happens The society must give customers prior notice before changing the cost. The bomb exploded without any prior warning. → prior
Examples from the Corpus
without ... prior warning• Note: Don't ever send an attachment of more than a few hundred kilobytes without prior warning or agreement.• You can imagine my surprise, then, when Pikey, without prior warning, started to hum like a top. 