ROME — Hundreds of migrant farmworkers walked off tomato fields in southern Italy on Wednesday to protest their working conditions after two road accidents killed 16 African laborers in 48 hours, adding a volatile new element to Italy’s wrenching debate over illegal immigration.

“We are not slaves,” the workers chanted as they marched in the red caps that protect pickers from the sun, and have become a symbol of their battle against day-labor exploitation in the province of Foggia.

The deaths dominated prime-time television this week and were quickly seized upon by the hard-line interior minister, Matteo Salvini, who promised to stop the exploitation by breaking up the ghettos where many migrants live.

“The fight against the mafia and exploitation are priorities of mine and of the government,” Mr. Salvini said on Tuesday, as he met with representatives of the African workers.