The Communications Workers of America, which represents the 21,000 wireless workers striking in 36 states and Washington, D.C. took credit for sporadic store closings from Montana to Chicago to Bangor, ME.

Still, AT&T said the “vast majority” of its stores were open despite the first labor strike against the company in four years. “We’re committed to delivering the best service we possibly can this weekend,” a spokesman said. “We’re open for business.”

The striking wireless workers, whose contract expired in February, walked off the job on Friday afternoon after AT&T failed to meet a union-set deadline for a new agreement. They have been joined by about 17,000 striking workers in AT&T’s traditional wireline telephone and Internet business in Nevada and California who have been working without a contract for over a year. Additional workers in the wireline business in Connecticut and the DirecTV unit in California are also on strike, the CWA says.

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The picket lines attracted support from members of other major unions, including the Teamsters, American Federation of Teachers and the AFL-CIO. Sen. Jeff Merkley (D-Ore.) also walked with the strikers on one picket line in Portland, Oregon.

The workers say AT&T has not made a fair contract offer. They want better wage increases, no healthcare contribution increases, and better job protection against outsourcing–both for call center jobs that could be moved overseas and retail store jobs shifted to third-party chains. The rate of sales commissions is also a key issue for retail store employees.

AT&T says it has offered “generous” wage and pension benefit increases and healthcare benefits similar to what other unionized employees have accepted around the country.

The strike, one of the largest in the U.S. in the past decade, is expected to end on Monday morning. That’s considerably shorter than the seven-week strike by 36,500 Verizon (VZ) workers last year. But the Verizon strike, which ended with workers getting a better deal than the company had been previously offering, helped inspire the AT&T (T) workers to walk out.

Until now, AT&T had enjoyed a long run of labor peace. The carrier hasn’t seen a labor strike since 2012, and that one lasted only two days. And a recent four-year contract ratified in April by 20,000 workers in Arkansas, Kansas, Missouri, Oklahoma, and Texas marked the 28th straight deal approved by AT&T and its unionized workers since the start of 2015. As part of the deal, AT&T agreed to hire 3,000 people locally for jobs that had been outsourced, mostly overseas.