It was not clear if Sarkozy would be charged during the hearing, which is investigating false accounting during his failed election campaign that allowed him to greatly exceed spending limits.
The case hinges on the activity of a PR firm, Bygmalion, which organised some of Sarkozy's campaign appearances and is accused of a vast system of false accounting.
Campaign spending limits were fixed at 22.5 million euros ($25 million), and Bygmalion is accused of charging some 18.5 million euros to Sarkozy's party -- then called the UMP, but since renamed The Republicans -- instead of charging the money to the campaign.
Several employees at Bygmalion, including the company's accountant, as well as a leading member of Sarkozy's campaign team have admitted to the existence of the fraud, though none have accused the former president of knowing about it.
Sarkozy, who led the country from 2007 before losing to Francois Hollande in 2012, has always denied any knowledge of the false accounting.
He said he was retiring from politics after the election but made a comeback just two years later, returning to lead The Republicans and attempting to position himself for another run at the presidency in 2017.
Despite his adamant denials, the investigation has found that Sarkozy had asked for more campaign events in mid-March 2012, around two months before the vote. His campaign director,
Guillaume Lambert, has told police he warned Sarkozy at the time of the risk of breaching financing limits.
Questioned by police in September 2015, Sarkozy said he did not remember the warning, and described the controversy as a "farce", putting the responsibility squarely on Bygmalion and the UMP.
Since then, however, the investigation has widened beyond Bygmalion and is looking into a further 13.5 million euros in campaign spending by the UMP, of which only 3.0 million was declared at the time.
A total of 13 people have been charged from Bygmalion and the UMP with fraud, abuse of confidence or illegal campaign financing.