THE CANADIAN PRESS/Jeff McIntosh - The Canadian PressCALGARY — Intense bargaining between WestJet and the union representing its flight attendants ratcheted up further on Thursday after CUPE issued a 72-hour strike notice, paving the runway for a possible airline shutdown during the busy summer travel season. The Canadian Union of Public Employees cancelled a news conference in Calgary on Thursday morning, saying it wanted to focus on hammering out a deal. The union representing 4,400 cabin crew at WestJet said the two sides remain far apart on key issues. WestJet responded to the union's strike notice by issuing a 72-hour lockout notice. At the Calgary International Airport, WestJet passengers held a medley of emotions about the impending strike.