Oxfam is facing tough questions from its corporate backers following revelations of sex crimes committed by the charity's workers in Haiti and Chad.
The Times of London has reported that Oxfam sought to cover up misconduct by senior aid workers deployed to Haiti after the devastating 2010 earthquake that killed hundreds of thousands of people.
The aid workers -- including the Oxfam country director at the time, Roland van Hauwermeiren -- were accused of turning a villa rented by the organization into a makeshift brothel.
Oxfam is supported by dozens of big companies including Visa, Google, PayPal and Unilever. It spent over -300 million ($414 million) in its latest financial year to address poverty and help victims of conflict and natural disasters.
The charity raised -17.4 million ($24 million) from philanthropists, companies and foundations last year, according to its annual report.
Visa described the sex crimes revelations as "deeply disturbing."
"We are engaging with Oxfam to understand exactly what occurred and what recourse will be taken," Visa said in a statement. "We are committed to the highest standards of professional and personal conduct, and we expect the same from our partners."
Waterstones, a British book retailer, said it would stick by the charity for now.
"We listen to, and seek to understand, the assurances given by the Oxfam leadership and at this point remain committed supporters to the charity," Waterstones said in a statement.
Britain's Co-operative Bank said it was in touch with Oxfam and "closely monitoring the situation." Another partner -- London's Heathrow airport -- said it was "taking this matter very seriously."
Google, PayPal and Unilever did not respond to requests for comment. U.K. department store chain Marks & Spencer declined to comment.
The Times said a confidential report by the charity found that van Hauwermeiren, who resigned in 2011, paid women for sex in the villa the charity had rented for him during the Haiti relief efforts.
CNN has not independently reviewed the charity's internal report.
Van Hauwermeiren has not commented publicly since The Times report on Friday. CNN's attempts to reach him have been unsuccessful.
According to the paper, the report also found that "children may have been among those sexually exploited by aid workers," and that there had been a "culture of impunity" among some staff in Haiti.
Penny Lawrence, the organization's deputy chief executive, resigned on Monday.
"Over the last few days we have become aware that concerns were raised about the behavior of staff in Chad as well as Haiti that we failed to adequately act upon," she said. "It is now clear that these allegations -- involving the use of prostitutes and which related to behavior of both the country director and members of his team in Chad -- were raised before he moved to Haiti."
Oxfam has denied allegations of a cover-up, saying that as soon as it became aware of the allegations it launched an internal investigation resulting in the dismissal of four staff members and the resignation of three, including the country director.
The aid group also said accusations that underage girls may have been involved were not proven.
Government funding for Oxfam is also at risk.
The U.K. government's International Development Secretary Penny Mordaunt warned on Sunday that Oxfam could lose millions of pounds in public funding because of the scandal.
Oxfam received around -32 million ($44 million) from the government in the last financial year, according to public records.
A spokesperson for the European Commission said it would pull funding from any agency that's "not living up to the required high ethical standards."
Oxfam received just over -29 million ($40 million) from the commission in its latest financial year.
-- Angela Dewan, Bharati Naik and Chris Liakos contributed to this report.