A formal investigation has been launched into possible favouritism in the awarding of the contract for an event in Las Vegas at which President Emmanuel Macron was the star speaker when he was economy minister, reports RFI.
The move puts added pressure on labour minister Muriel Pénicaud, who at the time was head of the organisation that awarded the contract to advertising and PR giant Havas.
The findings of a preliminary inquiry, launched in March, have provided enough possible evidence to open a formal investigation into "favouritism and profiting from favouritism", the Paris prosecutors' office announced on Friday.
Macron received a rapturous reception when he spoke to start-up operators at a "French Tech night" at the Consumer Electronics Show (CES) in the US resort on 6 January 2015.
He had been flown in specially and the event cost 381,000 euros, of which nearly 100,000 euros went in hotel bills.
By law any contract of more than 90,000 euros should be put out to tender but, although two other operators - Apco and Publicis - were contacted, no call for tenders was made.
Havas was awarded the contract in December 2015.
An audit by E&Y (previously Ernst and Young) in July 2016 warned there could be grounds for legal action, noting that "no purchase order, estimate, signed contract or bill" had been found.
A search of the offices of Havas and Business France, the state-run body that awarded the contract, on 20 June turned up an email from communications director Fabienne Bothy-Chesnau that appears to show that Pénicaud, who was Business France's boss at the time, was aware of the problems.
"Muriel, who has been briefed by us, is doing nothing," it read. "So she will handle things if the CDC (Court of Audit) demands an explanation [...] It won't be because it hasn't been mentioned and mentioned again."
Pénicaud, who on Friday issued a statement "categorically" insisting she had done nothing wrong, claims to have "immediately" ordered both and internal and an external audit but, according to Libération newspaper, she did not inform her board of the problems until December 2016, nearly a year later.