Among the names of those called in for questioning is Claude Guéant, a former Elysée secretary-general and once Sarkozy's right-hand man.
One of the polling companies named in the investigation was owned by Patrick Buisson, a close advisor to Sarkozy.
It was revealed that the surveys conducted by Buisson's company were also paid for by media organisations, which means a double income for the same work.
When the anti-corruption body Anticor took over the case it also found that the surveys commissioned served no public interest.
For opposition politicians like George Fennec, regardless of which party is involved, the files are there and must be dealt with.
"It's a good thing the judges are moving forward with this case," he said.
This is one of several fraud probes targeting the former president or his associates.
Sarkozy made a dramatic return to politics last year.
Last July Sarkozy became the first former head of state to be taken into custody for questioning when he was charged with influence-peddling and violation of legal secrecy.
He is accused of conspiring with his lawyer to give a top job to a magistrate in exchange for inside information on another corruption probe related to campaign financing.
Magistrates are also investigating unproven charges that ousted Libyan leader Moamer Kadhafi financed Sarkozy's successful 2007 election campaign.
In a separate case, judges are investigating public relations company Bygmalion, which is accused of falsifying invoices to get round spending limits during Sarkozy's 2012 presidential campaign.
Now leader of the freshly renamed Les Républicains (the Republicans) party, formally known as the UMP, Sarkozy is expected to run again in the 2017 presidencial race.