Cahuzac, whose resignation in disgrace last March rocked President Francois Hollande's Socialist government, met today with magistrates investigating charges laid after he admitted to having secret foreign bank accounts.
The source said he was informed of the additional charge -- of making an "incomplete or deceptive asset declaration as a member of the government" -- at the meeting.
Once in charge of battling tax evasion and fraud, Cahuzac has admitted to repeatedly lying about overseas accounts in Switzerland and Singapore said to contain around USD 799,000.
The scandal shook France's government and damaged the squeaky-clean image that Hollande had sought to project, less than a year after he was voted into office.