A couple years ago Westjet had their own employees in Calgary providing ground handling to load planes, push planes etc, they had voted to unionize to Westjet outsourced to a company called Airport Terminal Services one of the larger ground handling companies in US/Canada.
The Airport Terminal Services workers ended up unionizing and the union and company have been in negotiations, but appears it's starting to get heated and union may issue a 72 hour strike notice if an agreement is not agreed on.
While the workers don't work for Westjet a strike would potentially delays Westjet flights in/out of Calgary.
The 2 sides are still talking so the 72 hour strike notice has not yet been issued. (also a chance if a strike did occur, the federal government could issue back to work legislation, they have done this in the past with Canada Post, Air Canada and other federally regulated industries that have gone on strike.)