An estimated 17,000 AT&T technicians in California and Nevada went on strike Wednesday, highlighting workplace tensions within the massive Dallas-based telecommunications giant.

The strike follows a protracted dispute between AT&T and union members affiliated with the Communications Workers of America, District 9, who have been working without a contract for nearly a year. Workers say they have been increasingly asked to perform the duties of higher-paid employees without the same level of compensation.

Union members also have been upset by AT&T’s closure of U.S. based call centers, including a facility near Anaheim, to hire workers in overseas locations. They contend that AT&T has moved thousands of call center jobs in recent years to the Philippines, Mexico and other countries.

Wednesday’s walkout, which began at 6 a.m., was to protest what the union said was AT&T’s demand that technicians who typically install and maintain the company’s U-Verse TV service also work on the cables, hardware and other infrastructure used to provide landline phone service (AT&T’s wireless division is not affected by the action).

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