Minnie Driver has become the first celebrity to quit as an Oxfam ambassador following allegations senior staff working in crisis zones paid for sex with vulnerable locals.
The Good Will Hunting star resigned after 20 years with the charity, saying she was "horrified" by the scandal.
In a statement published in an article in The Telegraph, then tweeted from her account, she said: "I am nothing short of horrified by the allegations against Oxfam International.
"In no uncertain terms do I plan to continue my support of this organization or its leaders.
"And though it is unfortunate that after 20 years I am no longer able to advocate and defend through this specific framework, social and economic injustice is more globally prevalent than ever.
"I certainly will not let the abhorrent mistakes of a troubling organisation stop me or anyone else from working with good people in this space to support a population of human beings around the world that needs our help."
The 48-year-old later tweeted: "All I can tell you about this awful revelation about Oxfam is that I am devastated. Devastated for the women who were used by people sent there to help them, devastated by the response of an organisation that I have been raising awareness for since I was 9 years old #oxfamscandal."
During her time as an Oxfam ambassador, Driver travelled to countries including Cambodia and Thailand to highlight the charity's work and has also performed at a fundraising concert.
The Charity Commission has now announced it has opened a statutory inquiry into Oxfam, and international development secretary Penny Mordaunt is due to give a speech today (February 14) threatening to cut government funding to charities who fail to put robust safeguarding measures in place.
She is expected to pledge £5 million in government funds to the Global Partnership to End Violence Against Children - a network of governments, aid agencies, foundations and researchers working to stamp out child abuse across the globe.
Oxfam has issued an "unreserved apology" to the Government, donors, supporters and the people of Haiti over its handling of incidents including the alleged use of prostitutes by workers in the earthquake-hit country in 2011.
Four members of Oxfam staff were dismissed and three, including country director Roland van Hauwermeiren, resigned before the end of the 2011 investigation.
According to The Times, Oxfam knew about concerns over the conduct of van Hauwermeiren and another man when they worked in Chad before they were given senior roles in Haiti.
Oxfam denies a cover-up.