Police searched the offices of the far-right Front National (FN) in Nanterre, near Paris, on Wednesday as part of an investigation into allegations the party’s European MEP's misused EU parliamentary funds.
The funds given by European Union are meant to be used to pay assistants of the party’s 23 lawmakers.
Many of the assistants have official roles within the party beyond their parliamentary duties.
The FN denies that it embezzled the millions of euros in funds, calling the search a "political operation."
Several high-ranking members of the party have been accused of commiting fraud regarding the financing of parliamentary and presidential elections in 2012.
The search of the party's headquarters came a day after investigators went through documents belonging to National Front co-founder Jean-Marie Le-Pen, the father of leader Marine Le Pen.
Marine Le Pen was questioned by judges probing her party for fraud in January, after she previously refused to appear before judges investigating the FN's financial sources.
Le Pen and her father have recently attracted the attention of prosecutors who suspect they undervalued their assets in their tax declarations.
A French financial body, the High Authority for Transparency in Public Life, estimates both Le Pens underestimated their wealth by a third - a figure of about one million euros ($1.1 million) for Jean-Marie and hundreds of thousands of euros for Marine Le Pen.
Marine Le Pen also faces another investigation for tweeting graphic images released by the DAESH terrorist group, including the beheading of American reporter James Foley.
She has also been locked in a vicious feud with her father, who was booted out of the party earlier this year after rehashing familiar comments about Nazi gas chambers being a "detail" of history and saying France should improve ties with Russia to save the "white world."
Last week, Marine Le Pen officially announced she aims to participate in France's 2017 presidential elections.