On Saturday Perry posted to her 60 million plus followers on Twitter: "Remember AUS anyone printing or posting unauthorized photos of me in a bikini from these DISGUSTING/PERVERTED OLD MEN is AGAINST my will!"

Perry was with her dance squad aboard a chartered superyacht on Saturday when her security guards discovered photographers were trailing them in another boat.

She also posted three photos of unidentified paparazzi she claimed had been "stalking" her at Queens Beach in Vaucluse the day before. She had only just arrived at the private property where she has been staying during her time in Sydney.

While Fawcett's image was not among the photos she posted on Twitter, she singled him out in another tweet.

Fawcett declined to comment on the legal letter when contact on Tuesday morning, however Fairfax Media understands it also claims Perry's tweet contained an "implied threat" and warned the singer legal action would follow if any photos of Fawcett were published.

No photos of Perry, naked or otherwise, have surfaced from the boat trip and it is unclear if any exist.

Perry plays a show in Sydney on Tuesday night before heading to Brisbane for the next Australian leg of her  Roar tour.

Comment is being sought from Katy Perry's management.