County Antrim has been selected for a postal experiment by the postal delivery company Consignia, formerly known as the Royal Mail.
The changes mean businesses receiving more than 20 letters a day will get their mail delivered between 7-9 a.m.
Domestic households will get it between 9 a.m. and midday.
It is thought a weekly charge for businesses and individuals receiving fewer than 20 letters to have their mail delivered before 9 a.m. will save the company _350 million.
Bill Jeffrey of the Federation of Small Businesses in Northern Ireland said small businesses would suffer if forced to pay a weekly fee.
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