Since Polanski was arrested in California in 1977 on charges of drugging and raping 13-year-old Samantha Gailey, now known as Samantha Geimer, five other women including Monnier have come forward to allege that he either raped or sexually assaulted them.
Oscar-winning director Roman Polanski faced mounting pressure Sunday after threatening to sue over claims by a former actress that he violently raped her in the 1970s, the latest in a string of sexual assault accusations against him.
The 86-year-old film-maker rejected the allegation, but few from the world of French cinema have come out in support of Polanski, who fled to France in 1978 after admitting to raping a 13-year-old girl at the Los Angeles home of Jack Nicholson.
Jean Dujardin, the star of Polanski's latest film, which comes out in France on Wednesday, has abruptly cancelled a prime-time interview on the TF1 television station set for Sunday.
And the French artists' guild ARP could meet soon to discuss his exclusion, its vice president told the Parisien newspaper.
An ARP spokesman later told AFP that although no board meeting had been set, "If we are going to decide on Roman Polanski's membership, we will do so with the approval of film-makers".
Valentine Monnier, a photographer and former actress, has accused Polanski, who is French-Polish, of an "extremely violent" assault and rape at his chalet in the Swiss ski resort of Gstaad in 1975, when she was 18.
Monnier said he tried to make her swallow a pill during the attack, and later made a tearful apology while demanding a promise that she never tell anyone.
"I thought I was going to die," she said in an open letter published by Le Parisien, which also interviewed her and said it had contacted witnesses who confirmed the account.
"Mr Polanski disputes in the strongest terms this rape accusation," his lawyer Herve Temime told AFP in a statement.
"We are working on the legal action to bring against this publication," he added.
The rape claim has rocked a French film industry already reeling after a top actress last week said she was sexually harassed by the director of her first film when she was just 12.
Adele Haenel, whose account has garnered an outpouring of support, on Saturday urged others to speak out in support of Monnier and "take notice of her story".
French prosecutors have opened a sexual assault investigation into Haenel's claims, even though Haenel herself never filed a legal complaint.
Polanski and his new film, "An Officer and a Spy", had already courted controversy in September when it was included in the Venice film festival, where it took second place.
Monnier, who acted in a few films in the 1980s, said the release of the film, about one of the most notorious errors of justice in French history, the Dreyfus affair, had prompted her to speak out.
"How could he benefit from public funds to instrumentalise history, and in doing so rewrite his own to cover up his criminal past?" she wrote, referring to French subsidies for film productions.
"He pummelled me until I gave in and then raped me, making me do all sorts of things," she added.
She had previously written to France's first lady Brigitte Macron, who forwarded two letters to France's equality minister Marlene Schiappa, who has pushed for new measures to combat sexual abuse.
Schiappa wrote to Monnier in March last year and hailed her courage "in daring to break the silence", though the alleged attack was beyond France's statute of limitations for prosecution.
But her account may prove a turning point for French cinema, where the MeToo movement against rape and sexual assault that roiled Hollywood has not prompted as deep a reckoning of abuses in the industry.
- Oscar outlaw -
Monnier is the first Frenchwoman to accuse Polanski of rape. Since he was arrested in California in 1977 on charges of drugging and raping 13-year-old Samantha Gailey, now known as Samantha Geimer, five other women including Monnier have come forward to allege that he either raped or sexually assaulted them.
He has denied all the claims, but they forced him to abandon the presidency of the 2017 Cesars, the French equivalent of the oscars, and the following year he was expelled from the US Academy of Motion Picture Arts and Sciences.
Alain Terzian, president of France's APC film promotion association which oversees the Cesars, which includes Polanski as a member, did not immediately respond to a request for comment.
Both France and Poland have refused to extradite Polanski to the US, where California prosecutors are pressing their case even after Polanski paid Geimer $225,000 in an out-of-court settlement in 1994.
On Twitter, Geimer criticised Monnier for not speaking up sooner.
"Taking heat for not being more supportive of accusers who use film release dates to schedule their revelations with the press & sat silently while I was called a liar & a gold-digging whore in 1977 knowing they may have prevented it, if they had the truth & my mom's courage," she wrote on Saturday.