It’s the company’s first strike in over four years.

NEW YORK — The Communications Workers of America union says that up to 40,000 AT&T workers started walking off the job Friday over contract fights with the phone company.

The union says employees will return to work Monday.

That includes 21,000 workers on the wireless side of the company, which the union says raises the prospect that some cellphone stores could be closed this weekend in Washington, D.C., and in the 36 states affected.

Among them is Wisconsin. The union plans picketing at at least 12 stores across the state, most of them in southeastern Wisconsin or Madison.

Representatives at three Milwaukee-area stores where picketing was scheduled to begin Friday afternoon said they remained open. A phone call to a fourth store, at 17365 W. Blue Mound Road, Brookfield, went unanswered.

Wireless workers want wage increases that cover higher health care costs, better scheduling and promises from the company to not cut jobs.

The transfer of call center jobs overseas and the shifting of retail to non-AT&T stores are key issues for workers, said Candice Johnson, communications director for the union, said.

AT&T, which netted about $13 billion last year on $164 in revenue, is “a very profitable company,” Johnson said.

“So we need to … see that the company understands why this, especially this issue about jobs, is so important,” she said.

An AT&T spokesman was not immediately available for comment.

Besides the wireless workers, some 17,000 other potential protesters come from AT&T’s…