Almost half the workers in Verizon Communications Inc.'s wireline telecommunications business went on strike Sunday as negotiations for a new labor contract failed.

The strike, involving 45,000 workers, is the first walkout that Verizon, one of the two big U.S. telephone network operators, has faced since 2000, when about 80,000 workers went on strike for about three weeks. The striking workers include about 4,000 in Maryland, said union spokeswoman Candice Johnson.

Verizon and two unions, the Communications Workers of America and the International Brotherhood of Electrical Workers, had been in talks since late June but were still far apart when their contract expired Saturday night.

The workers who went on strike are technicians and customer support employees in the wireline unit, which provides traditional phone services to homes and businesses in the Northeast as well as high-speed Internet and FiOS television service.

The two sides were unable to agree on issues related to health care contributions, pension plans and work rules, according to Verizon and the CWA.

Verizon is looking to keep costs in check at its wireline business, which has been declining for a decade as customers have disconnected their home phones in favor of cellphone and Internet services.

A representative for the CWA, which represents about 35,000 of the workers, said that bargaining talks were expected to resume Sunday while employees were told to start picketing as early as 6 a.m. outside their work locations.

"A strike is a hardship for all and not to be undertaken lightly," Jim Spellane, an IBEW spokesman, said in an email.

"I think that the fact that we are on strike instead of finalizing an agreement is a testimony to Verizon's intransigence throughout the process," Spellane said.

Union officials said Verizon wants to downgrade pension, medical and job-security benefits at a time when the company is making billions in profits and moving call-center jobs out of the country.

Among the changes it is seeking, Verizon said it wants to freeze employee pension plans and replace them with an "enhanced 401(k) plan." It also wants workers to contribute to health care insurance premiums.

"We've been sitting across the table from them for several weeks and they were asking for concessions in the amount of about a billion dollars, and they're a profitable company," said Denise Burns, president of CWA Local 2107, based in Annapolis. "We just thought it's time we made a stand."

Verizon spokesman Richard Young said in an email on Sunday afternoon, "As of now, talks are not taking place today. We're always willing to talk. We're willing to return to the bargaining table at any time.

"We're in the process of implementing our emergency action plans," Young added.

Verizon said late Saturday night that it had trained tens of thousands of employees, from retirees to management, to fill the role of the workers who are on strike.

"We are confident that we have the talent and resources in place to meet the needs and demands of our customers," Marc C. Reed, Verizon's executive vice president of human resources, said.

Workers represented by the CWA will get $200 a week in strike benefits starting on day 15 of the strike, if it lasts that long, according to the union. This rises to $300 a week if it lasts 30 days.

The IBEW said it did not have a strike benefit fund, Spellane said.

"Nevertheless, our members are overwhelmingly supportive of the strike, knowing that the future of collective bargaining at the company is at stake," he said.

Baltimore Sun staff writer Jay Hancock contributed to this article.