One of two magistrates handling the case ordered the trial on the charge that Sarkozy spent way more than he was entitled to, despite warnings from his accountants.
The source, who was speaking on condition of anonymity as is often the case in France when initial announcements of trials are made, said 13 others would also face trial over the affair.
Lawyer Herzog highlighted the fact that only one of the two magistrates in charge of the case signed the trial order.
"The clear disagreement between the two magistrates in charge of the matter is such a rare event that it is worth underlining, as it illustrates the inanity of the decision," he said in a statement.
The trial order comes at a time when French politicians face growing scrutiny over their personal and political finances in the build-up to this year's presidential election in April and May. Sarkozy's conservative predecessor Jacques Chirac was convicted in 2011,
Sarkozy's conservative predecessor Jacques Chirac was convicted in 2011, after his retirement, of misusing public funds to keep political allies in phantom jobs.
That was the first conviction of a French head of state since Nazi collaborator Marshal Philippe Petain in 1945.
Conservative Francois Fillon, who beat rivals including Sarkozy to become the centre-right's candidate in this year's race, has been engulfed by a scandal over payments of public funds to his wife and children.
Far-right presidential candidate Marine Le Pen is also being pursued by the
European Parliament to refund money paid to her bodyguard and another person.
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