The far-right Le Pen unexpectedly turned up at the tumble-drier Whirlpool plant in Amiens, in the northern rustbelt and whipped up passions among workers, accusing centrist frontrunner Macron of showing "contempt" by not paying them a visit.
"Emmanuel Macron is with the oligarchs, with the Medef (employers' association)...I am with the French workers," she said.
The 39-year-old Macron, seeking to counter-attack, later turned up at the site in his hometown and was met with hecklers. A Reuters photographer there said some National Front activists were mingling in the crowd. Tyres were set ablaze in protest.
But Macron stood his ground for more than an hour putting his case to the workers, and the atmosphere gradually calmed during an encounter that was broadcast live.
He accused Le Pen, who was shown smiling and taking pictures with the workers, of cynically trying to exploit the situation and lying to workers when she said she would put a end to US-based Whirlpool's plans to relocate production to Poland.
He shook hands cordially with some workers before leaving.
"Mrs Le Pen came to take selfies for 15 minutes and then she was gone," Macron told a packed rally later in the nearby town of Arras. "She decided to stage a PR coup with the social situation that we know. She came to take advantage of poverty."
The clash between the two contenders for the decisive round of the presidential election on May 7 marked a sharp escalation in the campaign, with Le Pen taking the initiative and forcing Macron to step up his game after lying low for a few days.
Accusations of complacency
Macron, who polls consistently show will beat Le Pen by a comfortable margin in the run-off vote, had been accused by potential allies and some media of complacently acting as if victory was in the bag since coming first in an initial round of voting on April 23.
Le Pen's surprise visit at the Whirlpool strike site on the other hand showed the anti-immigrant leader was intent on waging an aggressive war of images. But some observers also praised Macron for standing firm against her ambush.
"It could be that Le Pen's coup failed in the end by giving Macron the political thick skin he was lacking until now," Christian Delporte, a historian and political image specialist at Versailles University, said.
When she arrived at the Whirlpool factory, she said: "When I heard that Emmanuel Macron was coming here and did not plan to meet the workers, did not plan to come to the picket line but would shelter himself who knows where in the chamber of commerce ... I considered it was such a sign of contempt for the Whirlpool workers that I decided to ... come here and see you."
Macron, who had been talking with workers' union delegates in a meeting room at the chamber of commerce across town, accused Le Pen of making empty, populist promises.
"Madame Le Pen is using the situation for political ends, stirring up crowds on a parking lot," he said.
"If she's elected, this company will close," he said, adding that he had first been to talk with union representatives to be able to discuss the issue in depth. "Madame Le Pen does not understand how this country works."
Later at the site he said: "When Madame Le Pen says we'll exit globalisation, she's lying to you," he told the workers. "If we shut down borders, thousands and thousands of jobs will be lost."
The Whirlpool factory in Amiens is set to shut down in June 2018 while the group beefs up its production in Poland.
Macron said that if elected president, the firm's redundancy plan would not be accepted if it was not good enough. Le Pen said she would not let the factory shut down at all and the state would, if she was elected, buy a stake in it if necessary.
Also on Wednesday, both contenders unveiled new campaign posters and slogans - "Choose France" for Le Pen and "Together, France!" for Macron - to take them into the run-off.
(Additional reporting by Pascal Rossignol and Myriam Rivet; writing by Ingrid Melander; editing by Richard Balmforth and Mark Heinrich)
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)