Organisers have said the Booker Prize is free from nepotism and favouritism.
There were concerns raised about the presence of a publisher on the judging panel for the 2019 award, who had worked with shortlisted authors.
Publisher and editor Liz Calder helped whittle down a long-list to the final six, which includes her previous colleagues Sir Salman Rushdie.
The shortlist also includes Margaret Atwood, who was once on her list at Bloomsbury.
Booker literary director Gaby Wood responded to concerns about impartiality saying: “I want to reassure you about the ethics of the process.
“Nepotism, favouritism, is absolutely not on.”
Wood further clarified that Sir Salman is a very outgoing person, and was likely to have friends on any Booker panel assembled from the literary world.
Calder said that she no longer had much affiliation with Sir Salman, and their one-time friendship had faded.
Chairman of the judging panel and Hay Festival founder Peter Florence said the prize was: “Absolutely clear on the ethical and practical side.”