"A very serious thing has happened! The decree on 'fiscal peace'... has been manipulated," Luigi Di Maio, who is also head of the anti-establishment Five Star Movement, wrote on Facebook in reference to the government's tax amnesty plans.
The amnesty has been a serious bone of contention between the movement and its far-right League coalition partner.
The idea is to resolve disputes with the taxman and recover some of the money lost to evasion, but critics of the government have said it is simply another amnesty for tax dodgers.
Dubbed the "fiscal peace" measure, it was one of the policy pledges in a government game plan drawn up by the parties, but the devil has proved to be in the detail.
While the League has previously said it wanted anyone with a dispute over up to €1 million to be able to benefit, the Five Star Movement insisted the ceiling to be set at €100,000, to thwart large-scale evaders.
Di Maio said on Wednesday that the decree had been tampered with after it had been given cabinet approval, to add "protection from punishment for evaders" -- though he did not provide any further details.
"I have never said we want to help mafia capital. We in the Five Star Movement will not vote for this measure if it comes to parliament like this," he said, adding that he did not know who was behind the changes.
"We are serious people who know nothing about manipulated decrees", the League shot back.
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Photo: Filippo Monteforte/AFP