Le Pen on Tuesday appealed to Mélenchon's voters to back her, accusing Macron of planning a war on their social conditions.
Many Mélenchon voters do not like either option for president: Emmanuel Macron or Marine Le Pen.
And they resent accusations of betrayal from politicians from mainstream parties who are urging them to support Macron to bar Le Pen's route to the Elysée Palace.
"We feel like we are being totally blackmailed into a choice between two persons who represent everything that we have fought against for most of us all our life," fervent Mélenchon supporter Alice Forge told RFI by phone on Wednesday.
"We are called fascists because we don’t want to choose between the oligarchy and the National Front but it was our party [La France Insoumise (Defiant France)] which is the one who has been fighting these ideas all year round, not just every five years."
Record of fighting far right
Karim Amellal, a professor at Sciences Po University and author, admits he is baffled as to why Mélenchon would give up fighting now.
“Honestly I don’t understand this strategy because Jean-Luc Mélenchon is known in France for his struggle against the far right and against Marine Le Pen," he told RFI.
Indeed, in the 2002 elections, when Marine Le Pen's father, Jean-Marie, made it to the second round, he called for a vote against the far right, which meant backing the conservative candidate Jacques Chirac.
“I think Jean-Luc Mélenchon is, of course, very disappointed not to have been in the second round but we don’t have a choice between liberalism and fascism," he said, in reference to Macron's unashamed pro-market principles.
"We have a choice between the Republic and fascism and, at that moment, the choice is obvious.”
Not for Alice Forge, though.
“For 15 years in France, we’ve had this blackmail over the fear of the National Front and it kind of allows all the other candidates not to have a real project. Macron is already opening a bottle of Champagne, as if he's won. He’s just not making any effort to try to interest all these people. We are 20 per cent [of voters]," she insists.
Mélenchon’s 19.6 percent of the vote Sunday is now a rich booty that Macron must surely be interested in.
But the centrist candidate's live TV appearance on Tuesday disappointed some Mélenchon supporters, who felt that he did not try hard enough to woo them.
"I need to hear some good reasons for me to vote for him," says Forge. "Apart from just avoiding fascism. Because this looks like fascism to me too. Maybe it’s a little bit less disgusting but it’s not really that much of a choice."
Members of Mélenchon's movement are currently being asked to choose online between a blank ballot, a vote for Macron or abstention.
“I personally don’t know what I will do yet," contines Alice. "Last year I protested against the law that Macron was passing very brutally on the labour law, so it doesn’t make any sense for me to vote for him and it doesn't make any sense for me to vote Marine Le Pen."
This quandary may have been avoided if the hard-left leader had given clear instructions on how to vote on 7 May, reckons Amellal.
"I think it is a bit irresponsible," he says, hinting that a blank vote or abstention may fuel the far right.
"We’ve known for years that abstention is at the benefit of the National Front." And Amellal is well briefed on the subject. His novel Bleu Blanc Noir predicted a Le Pen victory in the 2017 election.
"That’s why this hashtag movement #Sans moi le 7 mai (without me on 7 May) is quite dangerous because abstention serves the goal of the National Front," he says, hoping that, come the run-off, fiction doesn't become reality.
To read our coverage of France's 2017 presidential election click here