The US Postal Service intends to close more than half its mail-processing centres in a $US3 billion drive which is expected to shed 28,000 jobs.
Vice-President David Williams said the closures were designed to stave off bankruptcy next year.
Starting from next April, 252 of 461 centres will be closed.
The BBC reports the move could spell the end for next-day delivery of first-class mail.
Mr Williams said the volume of stamped mail had been steadily declining and customers were increasingly using the internet for bill payment and other communication.
first-class mail volume was almost 100 million items in 2006. The BBC reports the volume is down to 78 million and is expected to halve by 2020.
Under the changes, the Postal Service is also increasing the cost of first-class post by one cent on 22 January.
The agency reported an operating loss of $US5.1 billion in the last fiscal year. It is projected to make a record loss of $US14.1 billion next year.