A disgruntled AFL fan has written a scathing letter to the Carlton Football Club saying she will cancel her membership after the release of the club's stance on same-sex marriage.

The Blues released a statement on Twitter on Wednesday that failed to endorse the yes campaign on marriage equality, as Australians vote in a nation-wide postal survey on the issue.

The controversial stance has already been met by a flood of backlash with AFL fans taking to social media to dub it "weak", "hollow" and "disappointing" while others labelled it an attack on equality and human rights.

The AFL has backed the 'yes' campaign as have Western Bulldogs, North Melbourne and Collingwood in the past fortnight, joining long-term campaigners Sydney and St Kilda - who pioneered the annual pride game - on the issue.