Fast-food workers have won a major ruling that could improve their workplace conditions, wages and attempts to unionize. The general counsel of the National Labor Relations Board says McDonald’s must take responsibility for all of its workers, including those at restaurants owned and run by franchisees. Ninety percent of McDonald’s restaurants are franchises. Critics say that arrangement has helped the parent company protect itself from worker initiatives such as lawsuits and unionization drives. It has also helped deflect the ongoing movement for a $15-an-hour minimum wage, with McDonald’s arguing that franchisees set workers’ pay. In Tuesday’s ruling, the NLRB said McDonald’s qualifies as a joint employer in dozens of unfair labor practice cases, including for illegally firing or threatening workers involved in pro-union activity. The ruling comes just days after hundreds of fast-food workers from around the country gathered in Illinois for an organizing conference on their campaign for a $15-an-hour minimum wage.