Le Monde said a judicial investigation had been launched in April, leading to the appointment of a judge on the matter.
"The company acts within the law and will vigorously defend itself against any contrary allegation," Lagardere said in a short statement on Saturday.
Lagardere has been at odds recently with several shareholders including hedge fund Amber Capital which earlier this year filed a complaint. The dispute has been resolved since.
It is transforming itself into a joint-stock company, unravelling an arcane structure that had caused strife with shareholders.
(Reporting by Matthias Blamont; Editing by Frances Kerry)