George RR Martin is urging “every true fan” of science fiction to vote in the Hugo awards before the ballot closes at the end of July, for what the Game of Thrones author said was “proving to be the most controversial and hotly contested Hugo race in the award’s long history”.

The awards – which have run since 1953 and have been won by some of science fiction’s greatest names, from Frank Herbert to Philip K Dick – are proving contentious this year after a group of right-leaning authors calling themselves the Sad Puppies organised a slate of titles, which were voted on to shortlists by supporters. Several nominees have withdrawn in protest, objecting also to their inclusion on further lists organised by the provocative rightwing blogger Theodore Beale, known online as Vox Day.

George RR Martin says rightwing lobby has 'broken' Hugo awards Read more

The award-winning writer Connie Willis pulled out of presenting a prize at the August ceremony, saying: “I’ve essentially been told to engage in some light-hearted banter with the nominees, give one of them the award, and by my presence – and my silence – lend cover and credibility to winners who got the award through bullying and extortion. Well, I won’t do it. I can’t do it. If I did, I’d be collaborating with them in their scheme.”

Martin has been outspoken in his criticism of the campaign, saying in April: “I think the Sad Puppies have broken the Hugo awards, and I am not sure they can ever be repaired”. He described this year’s lineup as “the weakest Hugo ballot in recent memory, thanks to the Puppy slates”.

But he is still planning to participate, and this weekend urged others to join him and cast their vote before balloting closes at midnight on 31 July, because “this year, as never before, the voice and vote of every true fan is needed to help protect the integrity of the rocket”.

“The clock is ticking,” the bestselling author of the A Song of Ice and Fire fantasy series wrote on his blog, explaining that readers need to be a member of this year’s World Science Fiction Convention, Sasquan, to select their choice of winner – but they don’t have to actually attend.

“EVERYONE is welcome, despite what you have heard. (Just don’t be an asshole. Assholes get welcomed too, but the welcome wears out more quickly),” wrote Martin, pointing to the news that “more than 2,300 Hugo ballots have already come in”.

“Who are all these new supporting members? Are they trufans rallying to the defense of one of our field’s oldest and most cherished institutions?” he asked. “Are these the neo-Nazis and rightwing reactionaries we have been warned of? The truth is … no one knows … All I know for sure is that every vote will count … Let this be fandom’s finest hour. Vote.”

Titles in the running for the best novel award Hugo this year are Ann Leckie’s Ancillary Sword, Kevin J Anderson’s The Dark Between the Stars, Katherine Addison’s The Goblin Emperor, Jim Butcher’s Skin Game and Cixin Liu’s The Three-Body Problem.