The Paris prosecutor's office said on Wednesday that the party was under investigation over a suspected overbilling scheme by communications firm Riwal, with the French state paying out the extra funds as campaign reimbursements.
The "micro-party," named Jeanne, allegedly received illegal funding from the company, which has already been charged along with six other people in the inquiry.
Riwal is run by an old friend of FN leader Marine Le Pen, who once led an extreme-right group.
In a statement released on Wednesday, the FN said it will file an appeal against the charges.
"We are innocent of all the accusations against us," FN treasurer Wallerand de Saint-Just said on Wednesday.
Trouble in the right-wing camp?
The charges against the FN come just three months before France's regional polls, which are widely regarded as a preliminary test for the 2017 presidential election.
The inquiry hasn't involved Marine Le Pen, however. The daughter of former FN leader Jean-Marie currently has her eye on the presidential prize.
Despite its legal troubles and a family feud at the heart of the party, the FN's efforts to soften its image over the past four years appear to be paying off, with Le Pen's right-wing camp currently sitting comfortably at the top of France's opinion polls.
The FN is also under investigation by the European Parliament for suspected fraud amounting to 7.5 million euros ($8.1 million) over salaries paid to EU parliamentary assistants.
ksb/kms (AFP, AP)