An anonymous reader writes: Approximately 17,000 workers in AT&T's traditional wired telephone business in California and Nevada walked out on strike on Wednesday, marking the most serious labor action against the carrier in years. The walkout—formally known as a grievance strike—occurred after AT&T changed the work assignments of some of the technicians and call center employees in the group, the Communications Workers of America union said. The union would not say how long the strike might last. A contract covering the group expired last year and there has been little progress in negotiations over sticking points like the outsourcing of call center jobs overseas, stagnant pay, and rising health care costs. The union said it planned to file an unfair labor charge with the National Labor Relations Board over the work assignment changes. "A walkout is not in anybody’s best interest and it's unfortunate that the union chose to do that," an AT&T spokesman told Fortune. "We're engaged in discussion with the union to get these employees back to work as soon as possible."