For decades, Walmart has been one of the most formidable anti-union employers in North America. The retail giant built its reputation on low prices, sophisticated logistics and an aggressive opposition to worker organizing. Union drives at Walmart stores repeatedly ran aground when they met fierce employer resistance, legal battles and, in some cases, outright closures. That is what makes the recent contract victory by workers at Walmart’s distribution centre in Mississauga, Ont., so significant.