The Post Office is to cut 600 jobs in its cash handling business, according to unions.
The Communication Workers Union (CWU) and Unite called on the Post Office management to resign in protest at government funding cuts to the service.
The job losses being announced on Tuesday come on top of an expected loss of up to 500 frontline jobs from the franchising of 39 Crown Post Offices and the loss of over 50 financial service experts selling products in branches through a further savings programme, unions said.
The CWU and Unite warned the Post Office is in crisis and heading for "extinction" unless the Government and company change course.
Dave Ward, general secretary of the CWU, said: "With this latest round of job losses, the management of the Post Office has to face the fact that it is in crisis and heading for ruin.
"If they care about the future of the network they should resign in protest at the straight-jacket government cuts have left them in.
"The Post Office was split from Royal Mail in 2012 in the run-up to privatisation and we are yet to see a plan that will secure its future.
"With a cut in its funding from £210 million in 2013, to zero in 2019, these job losses show that under Business Secretary Sajid Javid's leadership the Post Office is heading the same way as the steel industry.
"This year alone CWU members in the Post Office face 500 frontline job losses in branches, 500 job losses in its cash handling business and the closure of their pension scheme. There is a perfect storm in the Post Office and our members will expect us to act to defend them."
Brian Scott of Unite said: "The redundancies of 79 Unite members announced today, take the total number of proposed job losses to 130 in the last two weeks.
"These proposals tear the heart out of the Post Office and put it on the road to destruction".
"The Post Office's business plan, which was agreed with the Government, has failed. Those at the top should accept the blame for that, but instead they are adopting a slash and burn approach in an effort to cover this up.
"We will not sit back and watch them destroy a public institution".
The CWU, the main union for postal workers, and Unite, which represents managers, called on the Government and the Post Office to halt cuts and to sit down with unions, customers, small businesses and communities, to put together a fresh strategy to develop new services and safeguard its future.
The Post Office's cash handling operation, Supply Chain, provides collection, handling and distribution of cash across the post office network.
The Post Office was briefing staff about the job losses on Tuesday morning, said the CWU.