Australia Post will only deliver letters every second day from next week, as a generational shift in the nation's postal services takes effect.

From Monday, 98 per cent of locations will have letter delivery reduced to every second business day, and delivery times for ordinary letters will be extended by a business day.

That means within the same state, letter delivery times will be 4 or 5 business days, depending on location, and 6 to 8 business days for interstate letters.

A daily priority letter service will remain available for customers who need fast delivery of mail, at a higher cost.

Requirements for Australia Post to maintain a minimum presence nationally and in rural, regional and remote areas will remain unchanged.

Separately, Auspost is raising the price of ordinary letter stamps from $1.20 to $1.50, and large letter stamps from $3.60 to $4.50.

The federal government agreed to change the law to loosen Auspost's requirements for letter delivery, acknowledging Australians send far fewer letters than they used to.

The postal service had warned without the change its "long-term viability" was at risk.

Auspost says the changes will allow it to focus on expanding parcel posting and collection places, which have become its major business.

Trials of the change resulted in postal workers being able to carry 20 per cent more parcels on each delivery.

Four in five households bought goods online last year, while letter volumes have fallen by about two-thirds since their peak in 2008.

Communications Minister Michelle Rowland said the way Australians used the national postal service had changed, and so Australia Post needed to be modernised.

"[These] changes reflect the way Australians now interact with Australia Post, and will help improve the company’s financial sustainability," Ms Rowland said.