"There is a serious doubt about the comprehensiveness, accuracy and sincerity of their declarations owing to the obvious undervaluation of real estate assets" held by the two Le Pens, said the High Authority for Transparency in Public Life in a statement.
The body also mentions the failure of Jean-Marie Le Pen, the firebrand founder of the far-right party, to declare certain property.
The High Authority "ruled it necessary to alert the financial prosecutor to these facts, which could represent criminal offences," said the statement.
The financial body estimates both Le Pens underestimated their wealth by a third - a figure of about one million euros for Jean-Marie and hundreds of thousands of euros for Marine.
Both could face a fine of up to 45,000 euros, three years in prison and a ban of up to 10 years from public life.
Jean-Marie Le Pen, 87, is accused of failing to declare a Swiss bank account and gold bullion, which already prompted a preliminary investigation into tax fraud in June.
