The Post Office is facing potential strike action as unions try to fight privatisation and cuts to jobs and pension benefits.

More than 80% of those who voted in a ballot by the Communication Workers Union this week backed strike action, but only 50.3% of the union’s 3,500 members who work for the Post Office took part.

The CWU is yet to set a timetable for any strikes, and is calling on the government to intervene because the service is on a “path to extinction”.

Unite, which represents Post Office supervisors and managers, will also ballot members on strike action on 5 September. It has also urged the government to investigate the service’s financial difficulties. It remains publicly owned after the part-privatisation of the Royal Mail postal service in 2013.

Dave Ward, the CWU’s general secretary, said: “The government has to step in, convene a summit of key stakeholders and hammer out with us and the board a strategy that will give the Post Office a future.

“It cannot wash its hands of this and simply stand by as a national institution goes under. Just as we have seen with Tata Steel, this is another clear example of the government having no plan whatsoever to stand up for British industry.”

Theresa May’s government, however, appears unwilling to get involved. A spokesman for the Department for Business, Energy and Industrial Strategy said: “This is an operational matter for Post Office Ltd. As its annual accounts show, there has been a continuing improvement in Post Office’s financial performance, and a reduced reliance on taxpayer support.

“Our investment has led to the most stable network for decades, 200,000 extra opening hours a week and more than 3,500 branches open on Sundays.”

The Post Office said that only 41% of the CWU’s membership had voted for strike action. It said it was happy to talk to the union but intended to continue its modernisation programme.

A statement from the Post Office made clear that any industrial action would not involve people working in more than 97% of the its 11,600-plus branches, and that it already had contingency plans to minimise disruption to services.

Kevin Gilliland, the Post Office’s network and sales director said: “We must continue with our plans to modernise our network and make it better for customers. We are taking the right actions to ensure that Post Office branches thrive for future generations.

“We halved our losses in 2015/16 and are making steady progress in ensuring our business is simpler to run, reducing costs to the taxpayer whilst at the same time modernising our network.”

The strike vote comes as about 3,500 workers face a cut in pension benefits as the Post Office tries to cut costs.

About half of its 7,000-strong workforce is being forced to shift from a final salary pension scheme to a defined contribution scheme, a move that unions say could cut retirement benefits by 30% or even more in some cases.

The planned pension cuts were announced just days after the Post Office said it would be looking to put 20 more Crown offices into private hands, taking the total this year to 85 in a process opposed by unions who see it as a form of backdoor privatisation.

The Post Office was already facing criticism after it agreed to hand over up to 61 branches to WH Smith in April, including some of the 39 Crown offices flagged up to be put into private hands in January. Before that, 50 Crown offices, which the Post Office runs directly, had been franchised or otherwise offloaded since 2013.

The Royal Mail is also facing a battle with its 140,000 workers after unions threatened a campaign of action against plans to cut pension benefits.