The grant-maker the Sackler Trust has said it will "pause" charitable giving in the wake of controversy surrounding its links to a pharmaceutical company.
The Dr Mortimer and Theresa Sackler Foundation has also called a halt to making any new donations.
Both organisations have said they will honour existing commitments.
The two UK-based grant-makers spent more than £11m between them in the financial year ending 31 December 2017.
The Sackler Trust gives grants to organisations in science, education, the arts, heritage, the environment and social good in England, Wales, Switzerland and the United States.
According to documents filed with the Charity Commission, it spent more than £45m in the three financial years to 31 December 2017.
It awarded 13 grants worth at least £150,000 in the year to 31 December 2017, as well as £1.4m in smaller awards.
Its main beneficiaries were Imperial College London and the Royal Museums Greenwich, which received £2.5m and £1.5m respectively.
The previous year its biggest grants were £6m to Sussex University and £3m to Moorfields Eye Hospital in London.
The foundation, which supports science, art and medical research, spent £4m in the financial year ending 31 December 2017, with £2m of this awarded to the Science Museum in London.
The National Portrait Gallery agreed not to accept a £1m grant from the trust last week after the US photographer Nan Goldin said she would refuse permission for a retrospective of her work at the gallery if it accepted the donation.
Goldin became addicted to Oxycontin, an opioid produced by the US-based company Purdue Pharma, which is wholly owned by the Sackler family.
Purdue Pharma is being sued in the US by the Massachusetts Attorney General’s Office, which alleged the company had created an addiction epidemic and "profited from it through a web of illegal deceit" – allegations the members of the Sackler family deny.
Dame Theresa Sackler said in a statement that the media attention "has created immense pressure on the scientific, medical, educational and arts institutions here in the UK, large and small", which was distracting them from their work.
"The trustees of the trust have taken the difficult decision to temporarily pause all new philanthropic giving, while still honouring existing commitments," she added.
"I remain fully committed to all the causes the trust supports, but at this moment it is the better course for the trust to halt all new giving until we can be confident that it will not be a distraction for institutions that are applying for grants."
A spokesman for the trust declined to comment further.
Dame Liz Forgan, former chair of the non departmental public body Arts Council England, said on Radio 4 today that private money had brought lots of new funding to the arts in the past 10 years, but it often had "dodgy features" that arts organisations "agonised" over.
She added: "There's just no such thing as an objectively justifiable blacklist beyond arms dealing, heroin and possibly cigarettes. After that the arguments become very tortuous."