Aid group Doctors Without Borders on Wednesday said it had acted on 24 cases of harassment or sexual abuse past year as British charity Oxfam faces a storm over its handling of a sex scandal.
The Charity Commission, which regulates the sector and will meet this week with Mordaunt, has asked Oxfam to urgently provide fresh information on the scandal in Haiti.
Ms Driver, who is best known for starring in 1997 film Good Will Hunting, said she had been "horrified" by the claims and would be stepping down as a celebrity ambassador after 20 years with the charity.
The charity group's name took another hit on Tuesday when Oxfam International's chairman Juan Alberto Fuentes Knight was arrested in his native Guatemala over government graft allegations unrelated to the sexual assault claims.
The actor added the controversy would not discourage her "from working with good people in this space to support a population of human beings around the world that needs our help".
U.K. Development Secretary Penny Mordaunt has warned that government funding to the group - some 31.7 million pounds ($43.8 million) - is at risk unless it comes clean about the allegations.
"Unless you report every serious incident or allegation, no matter how damaging to your reputation - we can not be partners", Britain's International Development Secretary Penny Mordaunt told a conference in Stockholm, according to extracts of her speech released by her ministry.
"We are very serious about it and we believe an example has to be set", he said.
Roland van Hauwermeiren, 68, whom Oxfam said was forced to resign as Haiti country director in 2011 after allegedly admitting hiring prostitutes, went on to become head of mission for Action Against Hunger in Bangladesh from 2012 to 2014.
The recent allegations concerning Haiti and Chad relate to Oxfam GB, one of the 20 affiliate organisations.
Priti Patel told Nick she wouldn't donate to Oxfam.
Another, Amira Malik Miller, said that such behavior was common by global aid workers in Liberia, and that she complained to Merlin about another colleague at the time. This epidemic is rooted in the unequal power relationships that enable powerful and predatory men to exploit women and children through bullying, sexual harassment and outright violence.
"However it would be even more tragically reprehensible if we allowed it to diminish the extraordinary efforts we collectively make, as members of the public who give and as humanitarian agencies who act, to help the people who most need our help".
Several Haitian NGOs said that the problems with Oxfam in Haiti were institutional.
A spokesman for Visa said: "We are engaged with Oxfam to understand what steps have been taken to address staff misconduct and ensure alignment with our own standards and values".