The chief of the French employers' federation warned voters on Tuesday against backing the far-right in regional elections this weekend, a rare move he said was justified because the Front National's economic agenda was not a "responsible" one, reports Reuters.
A newspaper and the Green party also urged voters not to vote for the FN, a measure of growing concern at polls that show the FN likely to win in two or three of 13 mainland French regions.
The anti-Europe, anti-euro FN's economic agenda is "exactly the opposite of what we need to kickstart economic growth in this country," Pierre Gattaz, head of France's employers' group Medef, told French daily Le Parisien in an interview.
The FN's economic agenda includes increasing import taxes, organising a referendum on leaving the euro, and reducing retirement age.
Gattaz took that stance with polls showing a rise in the FN's ratings this year against a background of a migrant crisis in Europe and after the Islamic State attacks that killed 130 people in Paris on November 13th.
While the Medef employers' group regularly lobbies the government on its economic policies, it usually stays clear of intervening in an election or telling voters who to back.
La Voix du Nord, a newspaper based in one of the regions where the FN is strongest and where its leader Marine Le Pen is standing, also took the unusual step for a regional daily of urging its readers not to vote for the FN.
"Marine Le Pen and the FN are not who they say they are," it said on its front page on Tuesday, the second straight issue targeted at the party.
The FN, which has seen its popularity rise since 2011 as Le Pen took over from her father Jean-Marie and strive to soften its image, won eleven municipalities in 2014 but currently rules no regional council.
Surveys show Le Pen topping the vote in the first round on Sunday in the northern Nord-Pas-de-Calais region and her niece Marion Marechal-Le Pen doing the same in southeast France.
While the second round is harder to predict, surveys see both winning on December 13th. A BVA poll on Sunday showed Le Pen winning that final round even if the Socialists decided to pull out of the race in the north to try to block her from winning.
The usually low-key election for regional administrations is this time a key test for France's main parties as they gear up for the 2017 presidential vote.
Winning in one or two big constituencies could be a useful stepping stone for the FN in 2017, one that it wants to use to convince voters it has the experience to rule the country.
President Francois Hollande's Socialists, who currently rule most regions, are set for defeat, and ex-president Nicolas Sarkozy's The Republicans are expecting a second victory this year after winning in another local election in March.
But the latest polls show the Socialists' defeat could be smaller than they feared and Sarkozy's wins not as big as he hopes for, partly because of the impact of the Paris attacks on a complex election.
How the three main parties fare in polls will also depend on negotiations between the two rounds.