Former French leader
If an appeals court upholds a judge's decision last year ordering the trial, Sarkozy could face a potentially embarrassing public ordeal as well as up to a year in prison if convicted.
Prosecutors claim Sarkozy spent nearly 43 million euros ($51 million) on his lavish re-election bid -- almost double the legal limit of 22.5 million euros -- via fake invoices which a public relations firm charged instead to his UMP party.
Sarkozy has angrily denounced the charges, saying he was unaware of the fraud by executives at Bygmalion, who are also facing trial alongside accountants and former UMP officials.
His defence team is also arguing on procedural grounds, saying Sarkozy has already been sanctioned for campaign overspending by France's Constitutional Council in 2013.
But that ruling involved just 364,000 euros of overspending, and came before the revelations of the "Bygmalion affair" and fake billings.
If judges decide this argument is valid, the matter could be sent to the Cour de Cassation, France's court of final appeal, which would delay any decision on whether a trial will be held.
Bygmalion executives as well as Jerome Lavrilleux, the deputy manager of Sarkozy's 2012 campaign, have acknowledged the existence of fraud and false accounting.
So far investigators have not determined who ordered the fraud, but an investigating magistrate in the case says Sarkozy, a lawyer by training, could hardly have been unaware of the financing rules.
"More than anyone else, he was supposed to know, respect and enforce... the legal requirements in this matter," judge Serge Tournaire wrote when ordering Sarkozy to stand trial in February 2017.
The appeal court's general counsel has taken a similar stance, writing in a requisition seen by AFP that Sarkozy "had knowingly given instructions leading to higher spending," a claim Sarkozy has denied.
'Restore my honour'
Sarkozy, 63, was president from 2007 until his defeat by Socialist rival Francois Hollande in 2012.
The rightwinger has been fighting legal problems on several fronts.
He is charged with corruption and influence peddling for allegedly offering to help a judge obtain a plum retirement job in return from secret information about another case.
That inquiry gave him the dubious distinction in 2014 of being the first former French president to be taken into police custody.
He has also been charged over accusations by former members of Moamer Kadhafi's regime that he accepted millions of the slain Libyan dictator's cash for his first presidential campaign in 2007 -- claims Sarkozy has vehemently denied.
He attempted a comeback last year, taking the helm of the Republicans party and hoping to be its presidential candidate, only to lose out to his former prime minister Francois Fillon.
In March Sarkozy said he was "finished" with politics after being grilled by investigators for two days over the Kadhafi charges, though he vowed to clear his name and "restore my honour".