Protesters have picketed an art world party as they called on Tate bosses to cut their ties with sponsor BP over the Gulf of Mexico oil spill.
A group of artists under the name The Good Crude Britannia was voicing its concerns as Tate Britain held its summer party.
The event was organised jointly to launch a major new display by artist Fiona Banner and 20 years of support by BP.
Figures such as playwright Caryl Churchill, cartoonist Martin Rowson and comedian and writer Rob Newman are among dozens of figures who have put their names to a letter protesting about the association.
They claimed the "BP logo represents a stain on Tate's international reputation".
Jane Trowell, of environmental arts campaign group Platform, said: "BP is trying to repair its tarnished reputation and buy our approval by associating itself with culturally important institutions like Tate.
"We hope that, as happened with the tobacco industry, it will soon come to be seen as socially unacceptable for cultural institutions to accept funding from Big Oil."
But Tate defended its tie-up with the oil company and said BP was "one of the most important sponsors of the arts in the UK".
It said regular reviews were undertaken to ensure compliance with its ethics policy.
"BP has worked with Tate since 1990. Its support has been instrumental in helping Tate develop access to the Tate Collection and to present changing displays of work by a wide range of artists in the national collection of British Art," a statement from the Tate said.
