The French prime minister's office has admitted to tipping off prosecutors about possible leaks to the website Mediapart - whose offices police attempted to search on Monday.
It's generated a major row about the journalists' right to keep their sources private - in a case that could prove very embarrassing to the French President.
Elena Casas reports from Paris.

At least 9 killed in hotel fire in India's Kolkata
Ebola cases in Congo exceed 5,000, government data shows
8 Israeli airstrikes hit Syria's Abu al-Duhur airbase, state TV reports
Indonesia earthquake death toll rises to 70, government aid arrives
China's torrential rains kill 10 in southwest as thousands evacuated
