Tiziano Renzi has become part of a wider probe into rigged tendering by Consip, the Italian administration's central purchasing office.
"This morning I received a notice to appear at the Rome prosecutors' office in regard to 'influence trafficking'," Renzi senior was quoted as saying by the Sole-24 Ore newspaper's website.
"Until this morning I was unaware even of the existence of this offence, and I certainly haven't committed it. My actions have been entirely transparent," he added.
His lawyer Federico Bagattini described the suspicions about his client as "totally incomprehensible", as the judicial document only mentioned the number of the law allegedly violated, according to the same media source.
"We will be getting in touch with the prosecutor to find out what the allegations are," Bagattini added.
Tiziano Renzi had already been the subject of a fraud inquiry, but last July a judge ordered the case to be dropped.
His son Matteo Renzi on Monday launched a comeback bid with a move to reassert his authority over his fractious Democratic Party before an election due in the next year.
Renzi, who quit as premier after losing a December referendum on constitutional reforms but who still leads the PD, secured the backing of the party's executive for an assembly that will set a date for the leadership vote.
Photo: Andreas Solaro/AFP