Los Angeles: Singer Lady Gaga has slammed music producer Dr. Luke and compared him to Ursula, the villainess who steals Ariel's voice in Disney's "The Little Mermaid", after he reportedly banned Kesha from performing at the Billboard Music Awards. The 30-year-old singer is horrified that Kesha -- who claims the producer sexually abused her for years -- has been banned from performing at the Billboard Music Awards on Sunday after his label Kemosabe Records "rescinded its approval" following concerns she would speak out about their ongoing legal battle, reports femalefirst.co.uk. Comparing Luke to Ursula, Gaga tweeted: "Listen Ursula, we want her voice back. #FreeKesha (sic)." Gaga -- who has been one of Kesha's most vocal supporters in her battle to be released from her contract by Luke's label -- also tweeted a link to a story about the controversy and wrote: "Isn't it strange that it's legal to own a woman this way?" After it was reported that Kesha was planning a statement performance in which she would make "direct references" to her battle with Luke -- who has denied all allegations against him -- Kemosabe records banned her from taking to the stage.