Czech Prime Minister Bohuslav Sobotka has announced that he will submit his government's resignation later this week because of a disagreement with Finance Minister Andrej Babis.
Mr Sobotka is unhappy about alleged unexplained business dealings of Mr Babis, a billionaire businessman.
The announcement comes less than six months before parliamentary elections.
Mr Sobotka has said he will meet the president in the coming days to formally submit the resignations.
The BBC's Rob Cameron in Prague says that Czechs have have had more than three years of more or less stable coalition government under Mr Sobotka, a mild-mannered social democrat.
But that stability has now come to an end because of the bitter rivalry between him and Mr Babis.
Their dispute came to a head over claims Mr Babis had avoided paying taxes on bonds issued by his own company.
Mr Sobotka argues that it is unacceptable for Mr Babis to remain as finance minister.
Mr Babis's centrist ANO party is far ahead of Mr Sobotka's centre-left CSSD in the opinion polls, our correspondent says, and this act of brinksmanship will be seen very much as pre-election manoeuvring.