French police are questioning left-wing leader Jean-Luc Mélenchon over fake-jobs allegations.
His France Unbowed party is being investigated for possible misuse of European Parliament funds.
On Thursday, prosecutors opened a separate inquiry for intimidation over his reaction to police searches at his home and party headquarters this week.
A furious Mr Mélenchon, 67, was filmed on Tuesday “I am the Republic!” and shoving a police officer.
He was shown confronting the officers, who had been despatched to gather evidence at his party’s headquarters.
“Get out of the way and open up this door,” he shouted at the officer, before he and a group attempted to force their way into the premises past the guards.
Inside, he told the prosecutor: “I’m the leader of an opposition group. You should not be treating me in this way!”
Mr Mélenchon – who carried 20% of the first round vote in last year’s presidential election – vented his anger on social media as the searches were happening, saying he was the victim of political persecution.
The new investigation alleged “threats and acts of intimidation against judicial authorities” and “violence against people carrying out public duties”.
There has been widespread condemnation of his actions from both politicians and the press.
Prime Minister Edouard Philippe said he was shocked by Mr Mélenchon’s reaction to police doing their job.
“In carrying out judicial procedures, the justice division is obviously independent and it is for us to protect that principle of independence,” he said.
On Thursday, prosecutors will question, the political leader over the alleged misuse of European Parliament funds to pay party employees in France. The funding of his 2017 presidential campaign is also being investigated.