The Communications Workers of America union set a deadline of 3 p.m. ET for reaching a new deal with 17,000 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. The deadline also applies to talks with about 21,000 workers in AT&T’s wireless business spread across 36 states and Washington, D.C. as those contracts expired in February. Additional workers in the wireline business in Connecticut and DirecTV workers in California also plan to walk out, the union said.

The union’s plan is to start the walk outs on Friday if no deal is reached and end the actions on Monday morning.

The workers say they want wage increases, no increase in healthcare contributions, and tighter job security protection against outsourcing—both for call center jobs that could be moved overseas and retail store jobs shifted to third-party chains. For store workers, sales commissions are also a hot issue. 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 CWA says the strike could lead to AT&T closing its wireless retail stores over the weekend. But the company says it has been training replacement workers and is ready for any job action. “Whether it’s hurricanes, floods, snowstorms or even a work stoppage, we’re always ready,” an AT&T spokesman says.

Get Data Sheet, Fortune’s technology newsletter.

The two units on the brink of striking follow AT&T’s recent run of labor peace. The carrier hasn’t seen a labor strike since 2012, and that 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. The company also reached a deal with the International Brotherhood of Electrical Workers in April agreeing to hire 1,000 workers and add a call center in Chicago.

But labor relations have been getting increasingly tense in the telecommunications industry since last year’s strike by Verizon workers that resulted in higher pay and better job security than the company was initially offering. At the same time, AT&T and Verizon have been under increasing pressure from Wall Street to cut costs as revenue from their traditional phone and wireless businesses has been shrinking.

Earlier this month, the AT&T workers took a page out of the Verizon (VZ) worker’s strategy for highlighting the issue of outsourcing. Verizon workers met with call center employees in the Philippines who answered customer calls. AT&T workers went to the Dominican Republic and met with call center workers there, some of whom are paid less than $3 per hour.

Still, even with the tense negotiations, AT&T (T) and its unionized workers have continually found a way to reach common ground over the past few years.