More than 50 authors have called on Edinburgh International Book Festival to cut ties with one of its sponsors over climate concerns.
A joint letter urges organisers to put pressure on Baillie Gifford over its investment in fossil fuels.
The festival director later called for an "open discussion" about the issue during the event, which started on Saturday.
Investment manager Baillie Gifford has said it is not a significant investor in fossil fuels.
The firm, which has sponsored the book festival for 19 years, said just 2% of its clients' money is invested in companies with some business related to fossil fuels compared to a market average of 11%.
Clean energy
A spokesperson added: "Of those companies, some have already moved most of their business away from fossil fuels, and many are helping to drive the transition to clean energy. Currently, 5% of our clients' money is invested in companies whose sole purpose is to develop clean energy solutions."
The BBC says Zadie Smith, Ali Smith and Gary Younge are among those who signed the open letter.
It comes after climate activist Greta Thunberg cancelled an appearance at the event.
The authors of the letter expressed solidarity with those harmed by the climate crisis.
Edinburgh-based author Mikaela Loach, who is due to appear at the event, said organisers "must stand by their 'climate positive' commitment and drop Baillie Gifford as a sponsor".
Novelist Yara Rodrigues Fowler added that recent global wildfires, flooding and extreme heat showed the destruction being caused by the fossil fuel industry.
Lifeblood
Festival director Nick Barley thanked the writers for the letter and described them as "the lifeblood of this festival".
He added: "We fully acknowledge your concerns about the devastating impact of fossil-fuel exploitation on the climate: as individuals and as a charity we firmly agree.
"For these reasons we promise to think about your letter carefully. The last thing we want is to let anyone give the impression we are on opposite sides."
However, Mr Barley warned the arts organisation would not have enough funds to operate without private sponsorship.
He also said Baillie Gifford was investing in companies that were seeking to resolve the crisis, such as Danish windfarm specialist Orsted.
Open mind
Mr Barley urged the writers to discuss their concerns during the festival and vowed he would "keep a open mind" about how to proceed.
Greta Thunberg had been due to speak at an event, but pulled out after accusing the sponsors of "greenwashing".
The Edinburgh International Book Festival runs until August 28. It will feature more than 500 events and 550 authors.