By Naomi O'Leary
ROME (Reuters) - The leader of Italy's 5-Star Movement has criticized party lawmakers for what he says is their lax stance on immigration, an issue that threatens to divide the party that took a quarter of votes in February's deadlocked elections.
The death of hundreds of migrants off Italy's coast last week prompted two 5-Star senators to propose reforming a law - hated by the left - that criminalizes irregular immigration.
Five-Star leader Beppe Grillo, who faces growing dissent from a minority inside the movement critical of his autocratic style, said he opposed the move and that the senators had no right to imply their opinion was official party line.
"This amendment is an invitation to migrants from Africa and the Middle East to head for Italy ... How many immigrants can we accommodate if one Italian in eight does not have money?" Grillo wrote on his blog.
"Their position ... is entirely personal. It was not discussed in an assembly with other 5-Star senators, it wasn't part of the program voted for by 8.5 million, it wasn't subjected to any formal internal approval."
Refusing to back any government led by traditional parties, 5-Star declined to go into coalition with the center-left Democratic Party of Prime Minister Enrico Letta. But its mass support could give it a decisive role in the future.
Grillo did not run for election, and runs the party from outside of parliament, using a scathing political blog and popular public appearances to express his views.
His support for the 2009 immigration law was met with surprise and disagreement from many supporters and went against a wave of demands for reform following the tragedy off the island of Lampedusa last week.
Fishermen said they were reluctant to go to the aid of the ship because of the law, concerned that they could face criminal charges of aiding illegal immigration if they helped.
The survivors of the shipwreck were put under investigation, potentially facing fines of 5,000 euros ($6,800) and forced repatriation.
"It was a little too hasty," 5-Star lower house leader Alessio Villarosa told reporters of Grillo's blog post, saying the proposal to overturn the law would go ahead.
Opinion polls taken before the row showed support for 5-Star at between 20 and 24 percent, down from the 25.5 percent it took in the February election.
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(Editing by Catherine Hornby and Robin Pomeroy)