Former French president Nicolas Sarkozy is to be formally investigated in connection with a case of alleged illegal party funding involving the country's richest woman.
Under French law, a formal investigation is the final step before a suspect can be accused of a crime, the ABC reports.
Mr Sarkozy's lawyers said they would appeal against the decision to investigate him over allegations he took advantage of elderly L'Oreal heiress Liliane Bettencourt when she was weakened by poor health.
The former French leader, who only this month hinted he could make a political comeback, has repeatedly denied taking campaign funds from Ms Bettencourt.
Mr Sarkozy was unexpectedly summoned to the Bordeaux offices of Jean-Michel Gentil, the judge in charge of the case, for face-to-face encounters with at least four former members of Ms Bettencourt's staff.
The surprise confrontation came over claims he had accepted envelopes stuffed with cash from one of the world's richest women to fund his 2007 election campaign.
Investigators suspect up to four million euros of Ms Bettencourt's cash made its way into the coffers of Mr Sarkozy's UMP party.
The judge is seeking to establish how many times Mr Sarkozy had visited Ms Bettencourt during his successful campaign.
"Nicolas Sarkozy, who benefits from the presumption of innocence, had been notified that he has been placed under formal investigation for taking advantage of a vulnerable person in February 2007 and during 2007 to the detriment of Liliane Bettencourt," the Bordeaux prosecutor said in a statement.
Mr Sarkozy, 58, has always maintained he visited Ms Bettencourt's residence only once during the campaign to meet her late husband.
But members of the multi-billionaire's staff have contradicted his version of events.
Mr Sarkozy's lawyer Thierry Herzog lambasted the decision to pursue his client as "legally incoherent and unfair".
Ms Bettencourt is now 90. Medical experts say her mental capacity began to deteriorate from the autumn of 2006.
Mr Sarkozy lost immunity from prosecution when he was defeated in last year's presidential election by socialist Francois Hollande.