The raid at the party's headquarters in Nanterre, west of Paris, came a day after police searched the home of founder Jean-Marie Le Pen, as well as the office of his secretary and an accountant linked to the party.
The case relates to 20 assistants to FN members of the European Parliament in Strasbourg, who were also listed as party workers.
Investigators are trying to determine whether the FN drew European Parliament funds to pay for the assistants by giving them fake jobs in Strasbourg, while they continued to work for the party elsewhere.
The FN criticised the probe as politically motivated in a statement issued Wednesday, saying the French government was trying to "hinder, spy on, and intimidate the patriotic opposition".
Story continues below…
The case was initially launched by European Parliament anti-fraud authorities in early 2015, before the case was passed to Paris.