French National Assembly President Richard Ferrand, a close ally of President Emmanuel Macron, was put under formal investigation on Wednesday in a financial impropriety case, the assembly said.
In a statement on Thursday, it said that Ferrand, who denies any wrongdoing, would use the procedure to defend himself and was confident the case would be dropped.
Under French law, being put under formal investigation means there is "serious or consistent evidence" that points to probable involvement of a suspect in a crime.
It is a step toward a trial, but many investigations have been dropped without going to court.
(Reporting by Leigh Thomas; Editing by Himani Sarkar)