Wallerand de Saint-Just was charged on Monday with misuse of assets and cited as an assisted witness - which leaves the door open to future action - in charges of complicity in fraud.
Six other people, including FN vice-president Jean-François Jalkh, have already been charged in the case.
The party is accused of overcharging candidates in the 2012 general election for campaign material produced by its own events organiser, Riwal, so as to claim the money back in state subsidies to parties that win more than five per cent of the vote.
The FN, Riwal and Jeanne, a fund-raising organisation set up by party leader Marine Le Pen, have also been cited in the case.
Investigators also suspect that Riwal was used to subsidise Jeanne and the FN by paying rent, salaries and running costs.
The far-right party denies all the charges.
Pointing out that regional elections, in which the FN hopes to do well, are due in December, vice-president Florian Philippot on Tuesday claimed that the case was "political", orchestrated by Taubira "who has never concealed the fact that she is a fierce opponent of the Front National".
The national election accounts committee had approved the party's accounts for the 2012 election, he said.
The fact that Taubira last week lifted his immuity as a Euro-MP in a case of libel against the state of Qatar was further proof of a plot, he added.
The FN is also under investigation by the European parliament for suspected fraud totalling 7.5 million euros over salaries paid to EU parliamentary assistants.