The vote was held on the movement’s digital platform from 9:00 am until 7:00 pm, and all M5S supporters who are subscribed to the platform had the chance to cast their vote.
The result will determine how M5S senators will vote when a parliamentary committee meets on Tuesday to decide whether to block the possible trial against Salvini.
Prosecutors in the Sicilian city of Catania want to continue an investigation into alleged abuse of power and possible kidnapping against the League’s leader, who is also deputy prime minister alongside his coalition partner, M5S leader Luigi Di Maio.
The charges laid against Salvini are related to the rescue in August of 190 people by Italy’s Diciotti coast guard ship, who were left stranded at sea for five days.
Thirteen migrants with health problems were disembarked on Lampedusa island in Italy’s southern tip.
The ship then headed to Catania, but was blocked for another five days before the remaining 177 migrants were allowed to disembark.
The permission only came once Salvini had been assured other European countries would take the migrants in.
The question posed in the M5S’ online vote read: “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?”
A majority of “Yes” votes will stop the investigation, while more “No” votes will allow prosecutors to continue, according to the platform.
The final word on whether Salvini will be stripped of his protection lies with parliament.
A “Yes” vote in parliament allowing a possible trial against Salvini is likely to cause tension within the government.
Formed in June 2018, the populist government has faced internal conflict in recent weeks, with the League and M5S clashing over key policies and electoral pledges.
Political commentators claim the coalition government is at risk of collapsing.
Salvini, whose League party has powered ahead of the M5S in the polls, said on Sunday he was not worried about the vote because he had “given [his] word” that the government would not fall.
“If, in order to defend my country’s borders, the safety of Italians and national interests, I must face charges and investigations, I’m very ready to face them,” Salvini said.