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".
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".