Once the frontrunner, Fillon is mired in a scandal over his wife's pay, and his campaign has been in serious trouble since he learned this week that he could be placed under formal investigation for misuse of public funds.
After a string of resignations among advisers and backers, the 63-year old former conservative prime minister is banking on a rally of supporters in Paris on Sunday to show his detractors that he remains their best hope to win the presidency.
But as soon as he ended a campaign rally on Saturday at which he defended his political plans as the only credible future for the country, The Republicans party announced it was moving up a meeting of senior officials to discuss the latest developments by 24 hours to Monday.
"Given the evolution of the political situation just seven weeks from the presidential election ... the political committee, has been brought forward," it said in a statement.
Former prime minister Alain Juppe, who lost to Fillon in the November primary and has been widely touted to replace him should he step aside, is not attending.
Opinion polls continue to show Fillon would fail to make the second round of the April/May election. Instead, centrist Emmanuel Macron is consolidating his position as favorite to win a second-round head-to-head against far-right National Front candidate Marine Le Pen.
Fillon's backers have been on the offensive since the candidate revealed that he could be placed under formal investigation. They are hoping to get some 45,000 people at a rally in central Paris on Sunday to show he still carries favor among grassroots supporters.
But an Ifop poll of 1,002 people published on Saturday showed 71 percent of French voters want him to quit the race, up six points from an identical survey on Feb. 19.
It also showed support from within Republican voters falling to 53 percent from 70 percent two weeks ago.