The French financial prosecutor's office announced on Thursday it has launched a preliminary investigation into far-right leader Marine Le Pen and her father Jean-Marie Le Pen on suspicions that they misrepresented their wealth.
A French body in charge of transparency in public life lodged a case in December against the Le Pens, saying they may had underestimated their wealth held in common in 2014.
Marine Le Pen appealed to the State Council, France's highest administrative body, but the appeal was rejected.
"After analysis, the national financial prosecutor decided today to launch a preliminary investigation," the prosecutor's office said in a statement.
It said the probe had initially targeted Jean-Marie Le Pen.
"The scope of the investigation is now expanded to the misrepresentation of Marine Le Pen's fortune," it said.
Jean-Marie Le Pen, co-founder of the National Front, also known as FN, was excluded from the party last year by his daughter after several controversial statements.
He is suspected of aggravated tax fraud, aggravated laundering and misrepresentations to authorities.