As of October, Posti will deliver stamped mail three days a week instead of five, following parliament's approval of an amendment to the Postal Act on Wednesday.
The state-owned postal firm said mail recipients will not see any major changes, noting that the delivery speed will remain the same.
The postal service said that stamped letters account for less than three percent of Posti's total delivery volume. Over the past several years, Posti has reported physical mail volumes decreasing at a faster rate in Finland than in many other European countries.
"Digitalization, changes in customer behavior and tight competition have reduced the volume of letter mail delivered by Posti by nearly 70 percent over a decade," Posti said in a statement on Wednesday.
"The less there is to deliver, the higher the cost of each item," Posti added, noting that the reforms will reduce the need for state funding.
Newspaper delivery will meanwhile continue five days a week—including in rural communities.
"Five-day delivery for paper newspapers in sparsely populated areas will continue, as newspapers will be delivered on two weekdays with the help of the state's delivery support," Posti said.
While the changes are set to come into effect in October, the amendment still requires the approval of the president.