The allegation comes as Labor sought to torpedo the temporary changes, which are a response to the pandemic, that see the frequency of letter deliveries reduced and posties switching to vans or warehouses.

Australia Post has come under increasing pressure from the union, CEPU, who claim it was briefed on a new model that would see a quarter of posties made redundant - however, the government says 25 per cent of posties will be retrained and redeployed, not cut.

CEPU pointed to an internal report from 2018 as evidence the organisation had plans to cut back services.

The report included a proposal to slow down mail deliveries to save an estimated $200 million a year, but Australia Post did not go ahead with the plan at the time because of a potential "clear reduction in customer service" and "reputational risk".

CEPU communications union president Shane Murphy called on Australia Post to come clean with the Australian public on its real plans for jobs and services.

"This is proof that everything Australia Post is saying about the need to introduce these changes simply to get through the COVID-19 crisis is absolute rubbish," Mr Murphy said.

"These plans have been in place for years and now they're using the current crisis as cover to push ahead with them.

"This is nothing but a blatant attempt to axe jobs and cut back services in order to save a buck. Unless this regulation is disallowed, customers right across the country will be learning that the hard way very soon."

Labor sought to overturn the temporary changes in the Senate on Wednesday, however the move failed when One Nation backed the government.

Labor Senator Kim Carr said the temporary changes would "effectively allow the shutdown of rural outlets".

"Once that happens, try reopening a country post office or a rural outlet," Senator Carr said.

However, Australia Post categorically ruled out any forced redundancies.

"Union claims as many as one in four postie jobs will be impacted are false - we are not forcing 2000 of our valued posties into redundancies," Australia Post chief executive Christine Holgate said.

Communications Minister Paul Fletcher said the claim 25 per cent of posties would lose their job was "completely untrue".

"Temporary regulatory changes will allow Australia Post to redeploy 2000 posties from delivering letters to delivering parcels," Mr Fletcher said.

"That means more job security for posties - as they are redeployed to the growth part of the business."