Salvini has struggled to find his political touch this year and he had a setback on Wednesday when parliament voted to lift his judicial immunity, a move that could led to him being charged with illegally detaining migrants at sea.
But ministers can not be tried for actions taken while in office unless their parliamentary immunity is revoked.
A simple majority of 319 senators is required, with the result of the vote to be known around 1800 GMT, if not before.
The charges relate to the ship Gregoretti on which migrants rescued at sea were held for week because Salvini ordered it not be allowed to dock in an Italian port.
The firebrand politician served as deputy prime minister and interior minister in the previous Italian government, but pulled out in a bid to force parliamentary elections.
Prosecutors in Sicily opened a probe into conditions aboard the boat, where the scores of migrants shared one toilet.
On July 25, 2019, the Italian Coast Gaurd ship picked up 140 migrants trying to cross the Mediterranean.
In the case pondered by the Senate on Wednesday, migrants had been transferred to the Italian coast guard vessel after some of them were rescued by a cargo boat, while others were taken from their unseaworthy boat by an Italian border patrol vessel.
The then-interior minister's "closed ports" policy, aimed at stopping migrant arrivals from Libya, saw his popularity numbers shoot up.
In recent months, migrants arriving in Italy from rescue vessels have been quietly relocated to other European Union countries under an informal deal struck in September between Italy, Malta, France and Germany. But another judicial body, the Tribunal of Ministers, made a decision to proceed.
Salvini has proudly defended his decision, and his overall stance on immigration as interior minister.
"I want to be proud of what I did, with my head held high", Salvini told reporters while fellow senators debated his fate. "Clearly the request for me to be tried will pass".
Viti Crimi, interim leader of the anti-establishment 5-Star Movement (M5S), Salvini's former government partner, said "the League leader has been living in a confused state for months".
If convicted, Salvini faces 15 years in prison.
An Italian Naval officer saltes as the body of a person who died after a fishing boat carrying migrants capsized off the Libyan coast, is brought ashore along with 23 others retreived by the Italian Coast Guard vessel Bruno Gregoretti at Boiler Wharf, Senglea in Malta on April 20, 2015.
Senator Gregorio De Falco, a former coastguard commander, said Salvini's order to prevent migrants from disembarking was "an unnecessary cruelty".
Salvini, whose party recently lost a key regional election in Emilia Romagna, faces yet another hurdle on February 27.
The Gregoretti investigation echoes another case from earlier past year when magistrates sought to try Salvini over his decision to keep 150 migrants aboard a coastguard ship for five days in August 2018.