Royal Mail want to stop delivering on Saturdays and make its service Monday to Friday only as the company clings to survival.
Bosses have asked the government if they can implement the change as the struggling postal network urgently look to reduce its costs.
It comes after they announced it will make up to 6,000 job roles redundant by next August as part of plans to cut back.
The business wants to cut its total workforce count by 10,000 and plan to move from a six-days-a-week service.
However, parcel services would continue to run all days of the week.
Royal Mail previously warned it expects its full-year losses to hit £350million. They reported a £219m underlying operating loss for the six months to September 25.
Keith Williams, the non-executive chair of Royal Mail's owner International Distributions Services, said "urgent reform" was now needed.
He said: "The government has now been approached to seek an early move to five day letter delivery, whilst we continue to improve parcel services."
Simon Thompson, chief executive of Royal Mail, said: "We have always been clear we need change to survive.
"We have started turning the business around and will do whatever it takes.
"We would prefer to reach agreement with the Communication Workers Union (CWU) but in any case we are moving ahead with changes to transform our business."
But a government spokesperson said there are "no current plans to change the universal service".
They said: "While we recognise the issues that Royal Mail raise, there would need to be a strong case that showed changes would meet reasonable needs of users of postal services and ensure the financial sustainability of the universal postal service."
An estimated £70m impact from strike action is blamed for plunging its parent firm into the red.
Last month, troubled Royal Mail confirmed it will reduce its workforce as it warned of further financial losses.
The company currently employs 140,000 people.
Mr Thompson said: "This is a very sad day. I regret that we are announcing these job losses.
"We will do all we can to avoid compulsory redundancies and support everyone affected.
"We have announced today losses of £219 million in the first half of the year. Each strike day weakens our financial situation.
"The CWU's decision to choose damaging strike action over resolution regrettably increases the risk of further headcount reductions."
Royal Mail staff held the first of 19 strikes in a long-running dispute over pay and conditions in October.
