The two near-identical crashes, which came within 48 hours of each other outside the city of Foggia in the Puglia region, have put a spotlight on the plight of foreign seasonal tomato-pickers during harvest season.
"It's a mafia problem. In Foggia... there is mafia criminality that I intend to eradicate street by street, town by town, by all means legally available," Salvini said at a press conference in Foggia on Tuesday.
Salvini, who is also co-deputy prime minister and leader of the far-right League, said his anti-migrant campaign would starve criminal gangs of people to exploit.
He also blasted "unfair competition" from what he calls imports "forced" by the European Union, a favourite target of his.
The Foggia province hosts thousands of African migrants who spend the summer harvesting season picking tomatoes in blazing temperatures alongside workers from eastern Europe, typically Romanians, Bulgarians and Poles.
Although most of those working in the fields in Italy have regular papers, they rarely receive the benefits and salaries required by law, and many live in squalid conditions.
They are often at the mercy of day labourer recruiters -- sometimes linked to organised crime -- who operate as intermediaries and collect a portion of the workers' pay.
Fourteen workers -- all non-EU citizens -- were killed on Monday when the van taking them home from work smashed into a lorry transporting harvested tomatoes.
On Saturday, four African farm workers were killed in another collision with a tomato truck.
That crash provoked dozens of African workers living in one of the province's shanty towns to go on strike on Wednesday morning and march to Foggia.
On Tuesday Salvini said that mafia networks had benefited from "uncontrolled immigration".
"If there were not thousands of desperate people to exploit, they would have more trouble doing business," he said.
The 45-year-old also announced his intention to tackle the "importing of slaves" from within Europe, asking for more stringent checks from his Bulgarian and Romanian counterparts.
Salvini said that Italy's traffic police have seized 300 vehicles in the area in recent months, most of which were "vans registered in Bulgaria and without insurance", adding that the service had only 116 officers to control the province's roads.
He said that some Italian farmers should be labelled "outlaws because some use mafia methods to enrich themselves".
Salvini also claimed that the EU had helped create the situation that led to the use of what Prime Minister Giuseppe Conte called "slave labour" after his own visit to Foggia.
"If Europe didn't force us to accept the importing of Tunisian tomatoes, Moroccan oranges, Burmese rise and Canadian wheat maybe it would be easier for our farmers to live," Salvini said.