The head of the anti-establishment Five-Star Movement, Luigi Di Maio on Monday called on activists to attend protest rallies planned across Italy including one in Rome on 2 June - Republic Day.
"We are organising rallies and walkabouts in Italy's main cities - symbolic gestures, everything possible to affirm our right to determine our future in a peaceful way," Di Maio said live on Facebook.
"On 2 June, Republic Day, I invite everyone to come to Rome for a major event," Di Maio said.
"We need to be seen and heard, " he said.
Efforts by Five-Star and the far-right League - Italy's two populist parties to form a coalition government collapsed at the weekend.
Italy's president Sergio Mattarella rejected eurosceptic economist Paolo Savona - the populist pick for finance minister - prompting the populist premier-designate Giuseppe Conte's resignation on Sunday.
Mattarella said he could not appoint Savona to the post due to concern from investors at home and abroad, a veto which sparked fury from Five-Star and the League.
"Why don't we just say that in this country it's pointless that we vote, as the ratings agencies and financial lobbies decide the governments?" Di Maio said in a video on Facebook.
League chief Matteo Salvini also criticised Mattarella's decision, calling for mass protests and accusing Brussels and Germany of meddling.
Five-Star and the League can muster a majority in the hung parliament resulting from the inconclusive 4 March national election that has led to almost three months of political deadlock.
