Beppe Grillo, leader of Italy's anti-establishment 5-Star Movement, demanded that parliamentarians in his group declare their votes openly after some apparently defied party orders in a secret ballot to appoint the speaker of the Senate.
In a post on his blog late on Saturday, Grillo said 5-Star parliamentarians were bound to follow voting directions agreed by a majority in advance and indicated that he expected any members who failed to do so to resign.
"If anyone has not met this obligation, they have lied to voters and I hope they will take the necessary consequences," he said. He said he wanted 5-Star senators to declare their votes.
Several 5-Star Movement senators seem to have voted with the center-left alliance led by Pier Luigi Bersani in Saturday's vote to elect former anti-mafia judge Pietro Grasso as speaker of the Senate, despite instructions to cast an empty ballot.
The vote was one of the first pieces of business conducted by parliament since the inconclusive February election which gave Bersani control of the lower house but left him without the numbers to control the Senate and form a government.
The choice of Grasso, who made his name fighting the mafia in Palermo, as well as lower house speaker Laura Boldrini, a former spokeswoman for the United Nations High Commissioner for Refugees, represented a change from the career politicians who have traditionally been appointed speaker.
Grillo, whose movement rode a wave of public disgust at the political elite to win 163 seats in parliament and control the balance of power, has repeatedly ruled out helping the mainstream parties with any pacts or alliances.
Saturday's vote was the first test of how disciplined the deputies and senators from Grillo's movement will be during the battle to find a way out of the stalemate left by the election.
The fiery ex-comic, who has come down heavily on followers who have defied him in the past, has frequently been attacked over his authoritarian style. Former prime minister Silvio Berlusconi said on Saturday his movement was "like Scientology".
Italian newspapers seized on the apparent signs of division in the movement, although the group's Senate leader Luis Alberto Orellana denied there was any split in the ranks of his members, none of whom has any experience in parliament.
"We are not guided by remote control. All of us have our own sensibilities, our own conscience and Pietro Grasso is certainly not part of the old apparatus," he told the daily La Stampa.