On Wednesday, French prosecutors opened a probe into the wife of Fillon who in 1998-2002 was allegedly paid between 6,900 and 7,900 euros (up to $8,500) for working as her husband's parliamentary aide and in 2012-2013 received 5,000 euros gross per month salary at prestigious cultural magazine La Revue des Deux Mondes, owned by Fillon's friend Marc Ladreit de Lacharriere.
"The problem of Francois Fillon is a problem of the trust between the candidate and the French," Le Pen said.
The leader of National Front added that this facet of the scandal and the voters asking themselves if Fillon was the person they thought him to be was more important than deciding if married couples could work together.
On Friday, Jean-Marie Le Pen, former leader of French National front party and father of Marine Le Pen, took an opposite stance and lashed out at the investigation against Penelope Fillon.
"Being a lawmaker's wife should not preclude one from working as [his] assistant, I think. I find outrageous the offensive launched against the parliamentarians' freedom to choose and manage budget allocations," Le Pen, who is a member of European Parliament, said Friday on his personal website.
The first round of French presidential elections will take place on April 23, with the run-off scheduled for May 7.