French President Emmanuel Macron's chief of staff, Alexis Kohler, is under investigation for alleged influence-peddling and conflict of interest, reports BBC News.
The financial prosecutor's office said it was checking whether Mr Kohler had breached civil service rules when he was handling issues relating to the Mediterranean Shipping Company (MSC).
He has denied wrongdoing. His family has links with Italian-Swiss MSC.
He and Mr Macron both studied at the elite institutions Sciences Po and ENA.
Mr Kohler, 45, is one of the president's closest aides. The Elysée Palace dismissed the allegations against Mr Kohler as "completely unfounded".
A French anti-corruption watchdog, Anticor, filed a criminal complaint against him.
MSC secured several state contracts while Mr Kohler was a senior official in the economy ministry.