PARIS - The French presidential campaign lurched across another speedbump Wednesday as conservative candidate Francois Fillon defiantly vowed to stay in the race despite being notified that he may face preliminary corruption charges in two weeks.

The spring election to replace unpopular Socialist President Francois Hollande has been like no other, strewn with surprises and besmirched with corruption allegations against Fillon and far-right candidate Marine Le Pen of the National Front. Le Pen so far has managed to dodge investigating judges and maintain a top position in the polls.

Fillon, a former prime minister and once the front-runner in France's two-round April-May presidential election, announced that he was summoned to appear before judges on March 15 for allegedly using taxpayers' money to pay family members for jobs that may not have existed.

The right-wing Republicans party candidate denounced the summons, saying it amounted to a “political assassination.” Then he went further, saying that France's entire presidential election was being taken out by an over-eager judicial process that was bulldozing the campaign. He appealed to citizens to “resist” and judge for themselves.

Fillon's claim that his campaign was being targeted in order to sink it drew indignation from President Francois Hollande, who said the candidate has no right to “create a climate of mistrust ... to throw extremely serious accusations at justice and, more broadly, our institutions.”

With the governing Socialists trailing in polls and with a newcomer to politics, independent centrist Emmanuel Macron, sharing the lead with Le Pen, France's traditional left-right divide could be obliterated this year, upending politics as usual.

“I won't cede. I won't surrender. I won't withdraw,” Fillon told reporters at his campaign headquarters, denying guilt.

However, cracks within his own party quickly appeared, as one of his campaign officials, Bruno Le Maire, bowed out without hours, saying he can't follow a man who won't honour his word to withdraw if charged.

Fillon's important centrist backers, the UDI party, huddled to decide how to proceed.

Time is not on Fillon's side. The top two presidential vote-getters in France's April 23 ballot head to a presidential runoff on May 7.

A determined Fillon soldiered forward, visiting France's annual farm fair in Paris - a must stop for presidential candidates. He sipped milk with dairy farmers who have complained bitterly about the falling price of milk.

Dairy farmer Benoit Affaire appeared not too concerned about Fillon's troubles, saying if “the candidate is of value, is competent - their problems ... for me have no impact on the presidential election.”

Fillon is suspected of paying his wife Penelope and two of his five children more than 1 million euros ($1.1 million) over many years for parliamentary aide jobs that involved no sustained work. It is legal, and not uncommon, for French lawmakers to hire family members or close acquaintances to serve as parliamentary aides. But they must actually do the work.

The financial prosecutor's office, which has been investigating Fillon since Jan. 25, decided Friday to launch a formal judicial inquiry. The list of potential charges includes misappropriation of public funds, abuse of public funds and influence trafficking.

The situation has shocked Fillon's supporters, since he had a clean-hands image despite more than three decades in French politics, an arena peppered with corruption. It stung even more since Fillon has been a big proponent of cutting government spending.

The far-right's Le Pen is embroiled in her own set of corruption allegations, along with her anti-immigration National Front party. One probe is centred on her aide at the European Parliament, suspected of being paid from EU coffers without doing any work.

Le Pen - whose candidacy has not suffered from her legal woes - dismissed the investigation as “political manoeuvring.” She was a no-show at a summons to appear before investigators last month. Her lawyer, Rodolphe Bosselut, told BFM TV she is not obstructing justice but “a form of injustice,” with the election around the corner.

Le Pen's chief of staff, Catherine Griset, was handed a preliminary charge of receiving money through a breach of trust.

Fillon's conservative party, the Republicans, is in a bind with no time left to field another candidate before the April 23 first-round vote.

Despite his slip in polls, Fillon is the first in the field of candidates to accumulate the 500 signatures from elected officials in 30 regions needed to run. Fillon chalked up 738 as of Wednesday.

Dairy farmer Franck Debeaupuis was philosophical about Fillon's predicament.

“To be handed preliminary charges is not proof of guilt. There were many others before him,” he said. “In any case, he won't be convicted before the elections.”

The always-packed agriculture fair was less kind to Macron, the 39-year-old former French economy minister who got hit on the head with a raw egg.

“It's part of French political life. It always has been,” he said, chalking it up to passions unleashed by French politics.