Magistrates in France have placed Marine Le Pen under formal investigation.
This comes after preliminary inquiries into allegations that European Union funding had been misused by the leader of the far-right National Front.
The placement under formal investigation was confirmed by Le Pen’s lawyer, Rodolphe Bosselut.
He has told reporters he will launch an appeal against the move, describing it as a “violation of the principle of the separation of powers”.
The newly-elected MP was summoned to appear before financial investigators in Paris on Friday afternoon.
Le Pen denies any wrongdoing and laughed off the claims during the recent presidential election campaign.
The National Front leader brushed off the allegations as being politically motivated.
It is alleged that funds were used to pay Le Pen’s national staff.
The inquiry is reported to be investigating alleged “breach of trust”.
Earlier this month the European Parliament lifted Le Pen’s immunity from prosecution in a special vote.
The move was seen as a way for French prosecutors to continue a defamation action against her.
Le Pen is embroiled in legal action following criticism of the centre-right mayor of Nice, Christian Estrosi.
He sued Le Pen after she accused him of “being in league” with Islamist militants.
Le Pen lost the presidential election to Emmanuel Macron but recently won a seat in the parliamentary elections.
The National Front leader is also caught up in a case over Tweets of graphic images of executions by ISIL militants.
Le Pen claims all the legal cases being brought against her are for “political reasons”.