Supporters of scandal-hit French presidential candidate Francois Fillon are gathering for a rally in central Paris, in what is being seen as a crucial test of his popularity.
Calls have been growing for him to quit over allegations he paid his wife and children for work they did not do.
Mr Fillon has so far vowed to carry on, but in recent days several senior allies have deserted his campaign.
His wife said on Saturday that she did carry out parliamentary work for him.
In an interview for French magazine Journal du Dimanche (in French), Penelope Fillon said everything was “legal and declared” and he would have paid someone else to do it if she had not.
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His Republican party has brought forward crisis talks on the candidacy to Monday.
The former prime minister has seen his popularity slip in opinion polls.
The rally for Mr Fillon is due to start at 15:00 local time (14:00 GMT) at Trocadero Square near the Eiffel Tower.
The BBC’s Hugh Schofield in Paris says that if he can get a big turnout – 50,000 or more – then he may be able to argue that he has a bedrock of support among voters.
But if the turnout is disappointing then the pressure for him to go may be too much, our correspondent adds.
Mr Fillon tweeted (in French): “At the Trocadero, we will demonstrate the strength of the popular will.
“Hold on, like I’m holding on. France deserves our courage!”
Paris Mayor Anne Hidalgo, a member of President Francois Hollande’s Socialist Party, called on Mr Fillon to cancel the event.
In a Facebook post (in French), she said that its real goal was to show opposition to the judiciary, the police and journalists who were seeking to “bring to light the truth”.
A counter-demonstration, billed as a pot-banging rally against corruption by officials, is expected in the Place de la Republique, AFP reported.
Speaking to supporters in Paris on Saturday as he marked his 63rd birthday, Mr Fillon said that those attacking him over his presidential bid were “trying to kill a desire for change”.
The latest opinion polls suggest that he would be eliminated in the first round of presidential election voting on 23 April, with far-right leader Marine Le Pen and liberal Emmanuel Macron likely to progress to contest the election run-off on 7 May.
A survey published in Journal du Dimanche (in French) suggests that 71% of those polled want Mr Fillon to step down.
In another blow to Mr Fillon’s campaign, his spokesman Thierry Solere became the latest member of the campaign team to announce his departure on Friday.
Mr Fillon’s woes have raised speculation that Alain Juppe, another former prime minister whom he overwhelmingly defeated in November’s Republicans’ primary, could return to the race if he were to pull out.
Fillon France election: Candidate faces crucial test in Paris rally