Prosecutors in southern Italy are pushing for an investigation into Salvini’s actions after the head of the far-right League party refused to let migrants disembark from a rescue ship.
The Five Star Movement (M5S) and League have been governing in an uneasy coalition since June but frequently clash over key electoral pledges.
M5S, billed as an anti-establishment party, prides itself on honesty and has long railed against politicians who have used their parliamentary privilege to avoid trials. It previously said that any minister accused of a crime should resign.
Five Star Movement leader Luigi Di Maio. Photo: AFP
But the party seems reluctant to upset its coalition partner, and commentators think it is likely to vote to block the trial.
The M5S official blog told members this case was "different" from those where ministers had tried to get away with "bribes, fraud or rigging the markets", because Salvini was doing his job and "not acting for personal interest".
The movement's leader Luigi Di Maio has said Salvini was acting with their full support and that he would would stand trial alongside him.
The case concerns the stand-off over the Diciotti, which was left in limbo for ten days in August after taking onboard more than 150 people, including children, who Salvini refused permission to land in Italy.
The ship was eventually allowed to disembark in Sicily only after the Catholic Church had brokered a deal with Ireland and Albania to take the migrants in.
READ ALSO: 'Italian ports are closed', Salvini warns migrant rescue ship seeking shelter from storm
A Senate committee is scheduled to discuss the matter on Tuesday, after which the Senate will vote - with M5S senators taking their lead from the result of the online poll.
The final word on whether Salvini can keep his protection lies with parliament.
Photo: Alessandro Fucarini/AFP
The M5S poll, which is being held today, allows party members to say whether they think Salvini should be stripped of parliamentary protection, allowing a possible trial.
However, the poll question put to members was ridiculed by both M5S sympathisers and the opposition as being purposefully misleading.
"Was the delay in the disembarkation of the Diciotti, in order to redistribute the migrants in various European countries, taken in order to protect the interests of the state?" the question reads.
Answering "Yes" will stop the investigation, while "No" allows prosecutors to continue, according to the website.
Salvini, whose League party has soared ahead of the M5S in popularity in the polls, said Sunday he was not worried about the vote because he had "given (his) word" that the government would not fall.