ROME (Reuters) - An Italian Senate committee voted on Tuesday to block an investigation into accusations of kidnapping against Deputy Prime Minister Matteo Salvini over his decision to hold 150 migrants on board a ship for five days last August.

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The committee voted 16 to 6 to stop the investigation into Salvini, who is also interior minister and the leader of the hard-right League party which rules in a coalition with the anti-establishment 5-Star Movement.

The case has sown division within the government and in particular within 5-Star, which has built its support on pledges to bring transparency to Italian politics and has harshly criticized past parliamentary maneuvering to halt judicial proceedings against lawmakers.

Prosecutors in Sicily have sought permission to investigate Salvini for abuse of power and kidnapping over the case of migrants held on board the Diciotti coast guard ship.

When Salvini took office in June of last year, he blocked humanitarian ships carrying rescued migrants from Italy’s ports and said he would allow migrants on shore only if other European partners agreed to take them.

In the case of the Diciotti, migrants rescued at sea were allowed to disembark when Albania and Ireland offered to accept some of them and Italy’s Catholic Church agreed to take responsibility for the rest at no cost to the taxpayer.

The 5-Star leader Luigi Di Maio held an online ballot of the movement’s core supporters on Monday and 59 percent voted to protect Salvini. The movement’s senators on the Elections and Immunity Committee said they would honor that vote.

“We have provided the guarantee for this government to keep working,” Mario Michele Giarrusso, a 5-Star Senator who sits on the committee, said after the vote.

Opposition lawmakers from the Democratic Party (PD) protested loudly in the courtyard outside the committee room, holding up signs that read “shame” and chanting one of the 5-Star mottos: “Honesty, honesty, honesty!”

Salvini said he asked for parliamentary immunity because his decision to block the migrants was in the best interest of the country and was taken together with his allies. Prime Minister Giuseppe Conte and 5-Star have backed this position.

The committee ruling precedes a full vote on the floor of the upper house, which is due to be held by the end of March.

Some 5-Star lawmakers have indicated they want to see the legal probe continue, but the full senate is unlikely to reverse the committee decision because centre-right opposition parties have said they will vote in favor of Salvini’s immunity.