Cliff Benson, founder of the Sea Trust, said that his charity could not condone working with TUI because the holiday company organised visits to attractions where dolphins are kept in captivity.
"We could not possibly work with a company that makes money from dolphins held in captivity - it would be hypocritical," he said.
"We asked the campaign organisers if they would speak to TUI to see if it would be prepared to issue a statement condemning the practice of keeping dolphins in captivity. When they failed to do this, we pulled out. We are confident we have made the right decision."
Robert Hepworth, executive secretary of the UN Convention on Migratory Species, said: "We could not have an active partnership with extremists who were prepared to hijack the event to draw attention to their views."