The parliament is poised to vote on a M5S resolution on Tuesday that will recommend ending weapons deliveries to Ukraine to avoid hurting the prospects for peace.
Excerpts from the resolution, leaked to the media on Saturday, echoed the proposal of M5S leader Giuseppe Conte who suggested a vote back in May on cancelling arms supplies.
The proposal put the former prime minister on a collision course with top diplomat Luigi Di Maio, who accused his own party on Sunday of immaturity and undermining national security, according to La Repubblica daily.
His criticism reportedly provoked a lashback from M5S vice-presidents Riccardo Ricciardi and Michele Gubitosa, who suggested in interviews with Italian newspapers that Di Maio should leave the party.
An emergency meeting of M5S national council is scheduled for 9 p.m. (19:00 GMT) on Sunday. A split in Italy's largest party by parliament seats may push the country toward a new government crisis.