The Finnish Center Party withdrew its backing for Rinne, who is also leader of the Social Democratic Party, but pledged its continued support for government programs.
The Finnish parliament will begin a debate on an interpellation by the opposition conservatives on Tuesday. Many political observers predicted Rinne would resign before the debate as he would now be very likely to lose the vote of confidence.
However, Rinne said in a live national telecast on Monday night that he would not resign, but wanted to hear more from the Center Party.
The current situation was triggered by the recent massive postal strike. The ruling coalition had demanded Rinne to give an explanation for the government's statements and actions. However, the Center Party said the explanation was not acceptable.