Protests against Andrej Babiš were held across the Czech Republic.
The planned coalition between the ANO and Social Democrats would increase defense spending, social spending, and infrastructure investments.
The Czech Republic has been in the midst of a political deadlock for half a year, but this may soon end.
Forming a government with the Communists and SPD party would give Prime Minister Andrej Babiš's ANO party a parliamentary majority.
The ANO rejected the ČSSD's proposals on forming a coalition government.
During the Communist era, Zdeněk Ondráček was behind a crackdown on demonstrations against the ruling regime.
Jan Hamáček is the new chairman of the Czech Social Democratic Party.
Andrej Babis is attempting to form a new government before a new presidential term begins.