An angry backlash has erupted among UK authors who are increasingly frustrated at being asked to provide their time for nothing, whether writing, reading at literary events or judging book prizes.

Frustration spilled out on Facebook after a University of Cambridge professor of modern German and comparative culture, Andrew Webber, branded the acclaimed literary novelist Philip Hensher "priggish and ungracious" for refusing to write an introduction to the academic's forthcoming guide to Berlin literature for free.

Hensher said: "He's written a [previous] book about writers in Berlin during the 20th century, but how does he think that today's writers make a living? It shows a total lack of support for how writers can live. I'm not just saying it for my sake: we're creating a world where we're making it impossible for writers to make a living."

Hensher, who was shortlisted for the Man Booker prize in 2008 for his novel The Northern Clemency, a portrait of Britain's social landscape through the Thatcher era, wrote his first two novels while working a day job, but said: "I always had an eye to when I would make a living from it. If people who claim to respect literature – professors of literature at Cambridge University – expect it, then I see no future for young authors. Why would you start on a career if it's not just impossible, but improper, to expect payment?"

Author Guy Walters, this week vented his frustrations at a rising number of requests to work for free in an article for literary journal the Literary Review. In it, he cursed his own foolishness for having accepted an invitation to speak at Hay festival in return for six bottles of wine.

"The problem is not just festivals, it's across the lots and lots of different institutions, organisations, literary prizes and events who expect authors to do things for very little or no money, because it's an honour to do it," Walters said. "There's a romantic notion that authors work for the love of culture and high ideals, but it doesn't put food on the table. If you value culture, you must pay artists. It's a complete con and an absolute racket. There's a word for working for free: it's slavery."

In his Facebook post, Hensher commented: "Authors be warned – if you suggest that you want to be paid for your hard work, prepare to be insulted by Cambridge professors."

He received a flood of support from friends and fellow writers including the Guardian critic Nicholas Lezard and novelist Aminatta Forna.

"It's not reasonable to say if you're not being paid, you shouldn't complain and you shouldn't be angry. Nobody would say that about absolutely any other profession," Hensher added. "It's our duty as writers to place a value on our work, and not to allow it to be unreasonably eroded. There is increasingly a culture of consumers not paying for cultural products, whether it's downloaded music or free newspapers. You can have writers who do it in their spare time, who have independent means, or have literature written by people in institutions, but it's not going to lead to an improvement in literature."Walters, whose books include Hunting Evil, an account of Nazi attempts to escape at the end of the second world war, added: "I absolutely refuse to do anything for free, no matter what it is. It basically supposes that authors live in a rarefied world in which they don't need money. If you want culture to be enriched, you need to enrich authors."He said that publishers' advances had been reduced over the past decade, which added to the squeeze on authors' income, making payment for one-off freelance jobs all the more important.

Neither the Hay Festival director, Peter Florence, nor professor Webber were available for comment when contacted by the Guardian.

A Cambridge University Press spokesperson said: "We do, of course, pay our authors and other contributors royalties and other fees at a level that can be supported by the book in question. When we publish academic books, the audience for each book is naturally often relatively small. Most of our authors are practising academics whose main job is teaching and research, and who write for us primarily to promote the circulation of academic ideas. That is the purpose of the press, too: we exist to advance knowledge, learning and research, not as a commercial organisation. Some people who write for a living may naturally want to be paid for what they do at a level which is beyond the economic scope for these types of books, though we are delighted that others are happy to participate in our books, including Cambridge Companions, for other reasons."

• We published this response from Professor Webber in our letters section on 14 October.