The competition regulator has approved a 25 per cent rise in the price of postage stamps for ordinary letters to $1.50 next month.
The price rise comes just over a year after stamps for small mail letters last went up in price from $1.10 to $1.20.
Australia Post also intends to increase the prices for ordinary large letters up to 125 grams from $2.40 to $3.00, and ordinary large letters between 125 and 250 grams from $3.60 to $4.50.
There will be no price increases for concession stamps, which will remain at 60 cents each or five for $3 for eligible concession card holders.
The price of seasonal greeting cards will not increase either, remaining at 65c.
However, the Australian Competition and Consumer Commission has identified some concerns with Australia Post's financial modelling, and has made several recommendations for improvements, particularly if further price increases are proposed in the future.
"We don't object to Australia Post's proposed price increases on a cost-recovery basis," said ACCC Commissioner, Anna Brakey.
"However, our recommendations seek to improve how Australia Post incurs and accounts for the costs of its reserved letter services, so consumers are not paying more for stamps than they should."
The ACCC found declining letter volumes, combined with an increase of delivery addresses, continued to explain Australia Post's shortfall between its costs and revenue for the reserved letter service.
"We acknowledge the concerns raised in our consultation processes about the impact of the price increase on consumers and businesses, especially in light of cost-of-living pressures," Ms Brakey said.
The average Australian sends approximately 15 small letters a year, so the price increase would mean an additional cost of $4.50 each year.
The ACCC recognised consumers would be impacted differently depending on the number, size and type of letters sent, as well as their ability to access concession options.
Australia Post's proposed price change was outlined in a draft price notification to the ACCC in August last year and later revised in November and December.