But the outgoing Transport and Infrastructure Minister Maurizio Lupi, who has not been charged or placed under formal investigation, insisted his personal conduct had been beyond reproach.
"I am not here to defend myself against (criminal) accusations that don't concern me," Lupi said in his resignation speech to the lower house of parliament.
"I'm here to take political responsibility for the choices that I made and that my ministry made.
"I leave the government with my head held high."
Lupi's impassioned defence came as new leaks from a probe into the allocation of €25 billion worth of infrastructural contracts offered fresh evidence in support of claims the minister used his influence to arrange a temporary job for his son through a businessman and a company implicated in the scam.
Wiretap transcripts published by Corriere della Sera indicate he repeatedly discussed his son with a former ministry official, Ercole Incalza, who was arrested on Monday and is suspected of being the lynchpin of a corrupt network of top officials and businessmen that judges have dubbed "the system."
Lupi categorically denied the charge of nepotism, saying: "My son had no need of that. Had I wanted to do that, and I didn't, I could have done it (fix a job) myself far more easily," Lupi said.
The one error the minister did admit to was not insisting that his son give back a Rolex watch he was given as a graduation present by the same businessman who allegedly arranged his job, Stefano Perotti.
"I didn't ask him to give it back. If this was my mistake, I admit it," the 55-year-old told deputies, pointing out that the luxury timepiece was worth €3,500, rather than the €10,000 quoted by the media.
Incalza, Perotti and two others were arrested on Monday as examining magistrates in Florence placed a total of 51 people under formal investigation in connection with the public works probe.
The judges believe the four arrested men controlled the allocation of contracts in a way that enabled them to skim off between one and three percent of their value in "commissions".
Taxpayers incurred far greater costs because the skewing of fair competition for contracts is estimated to have increased the cost of the projects involved by as much as 40 percent.
Italy's pavillion at the upcoming Milan Expo 2015 world fair, sections of the high-speed rail and motorway networks, a new port on Sardinia and metro extensions in Rome and Milan were among the major works affected.
The Florence judges appear to have uncovered public sector corruption on a scale unseen since the "Tangentopoli" scandal of early 1990s in which half the country's lawmakers were indicted.
Prime Minister Matteo Renzi, who was made the anti-corruption fight a central plank of his premiership, reportedly demanded that Lupi quit as soon as the scandal broke. But he has yet to comment directly on an episode that has damaged his government's credibility and threatened to upset the balance of his coalition.
Lupi is a member of the New Centre Right (NCD), the junior partner in an alliance dominated by Renzi's centre-left Democratic Party (PD).
As such it would have been difficult for Renzi to force the minister out but the drip-drip of embarrassing leaks from the Florence investigation effectively did that job for him.