AceShowbiz - Rapper Riff Raff's upcoming tour of Australia and New Zealand has been axed following an allegation of sexual assault.

Eliza Stafford detailed her alleged encounter with the star in a Facebook post on Thursday, May 31, claiming he raped her in 2013.

The Australian woman, who was then 19, revealed she went to a Riff Raff show with her boyfriend and was invited backstage, where she was offered a shot from a vodka bottle that was sitting on the table. She alleges the drink was actually mixed with prescription cough syrup, which some people use to get high.

"I took the shot, it was syrup and I immediately asked what it was," she wrote. "Riff Raff and his support act told me that it was codeine and started laughing. I don't remember anything from that point. I woke up as Riff Raff was pulling out of me and getting in to the shower."

Following her Facebook allegation, bosses at booking agency Audipaxx issued a statement, which read: "We have been made aware of allegations made against Houston rapper Riff Raff. Audiopaxx takes these matters seriously and does not condone any of this alleged behaviour. In light of this, we have spoken to his management team and the scheduled tour of Australia and New Zealand has been cancelled, effective immediately."

Riff Raff has yet to comment.