Britain's deepening postal crisis is going national with a strike vote approved Thursday.

Postal workers agreed to launch a nationwide strike after months of rolling regional strikes over pay and job security that have already caused a backlog of undelivered letters and packages.

The Communication Workers Union said that 76 percent of more than 80,000 union members voted in favor of the action. The union must give seven days notice before any strike and Dave Ward, the deputy general secretary, said there was still a chance to reach an agreement.

The vote comes amid disputes over how to best modernize the mail service.

"We've seen cuts and increased workloads and now we need an agreed rollout of real modernization," Ward said. "Aligning the interests of customers, employees and the company as a whole is a prerequisite for the successful modernization of Royal Mail."

Business Secretary Peter Mandelson has refused to intervene, but the union says the government, which owns Royal Mail Group PLC, has a responsibility to act.

The union and the Royal Mail blamed each other for the dispute amid claims that postmen and women were being put under "unbearable pressure" to implement changes.

Mark Higson, Royal Mail's managing director, said changes were being made in response to falling volumes of mail. Letter volumes were falling by 10 percent a year as people switched to other forms of communication such as e-mail and texting, Higson said, and Royal Mail faces competition from other carriers for parcel delivery.

There have also been complaints from a number of communities, including those in some remote rural areas, because post offices have been shuttered as part of a cost-cutting effort. A number of services have been cut.

Royal Mail plans no more changes effecting workers this year, though more are planned next year, operations director Paul Tolhurst said.

"Change is a very difficult thing. Asking people to work an extra street is not easy. But we have to make sure our people work efficiently so we can deliver the best possible postal service," Tolhurst said.

As the strike threat looms, one of Royal Mail's biggest customers, online retailer Amazon, said it was examining options.

"We have not canceled any long term contracts with Royal Mail," the company said in a statement. "They continue to be one of a number of carriers that we use."

However, Amazon said it was working on contingency measures with other carriers.