WestJet flight attendants went on strike Sunday after the airline and their union failed to reach a new collective agreement. The airline said the stoppage had cancelled August long weekend travel for about 250,000 customers, with more flights at risk if the strike lasts. CUPE Local 8125 represents about 4,400 WestJet flight attendants. Affected passengers were to be notifiedWestJet said passengers whose flights are cancelled would be notified by email and text message. The airline said it would rebook affected passengers on the next available flight, including flights operated by other airlines.