Ashley - whose mother Alana was Rod's first wife - says he worked with Robbie on new single 'She's Madonna' before the 'Angels' singer asked the Pet Shop Boys to finish the track.
Ashley, 31, told Britain's Daily Mirror newspaper: "We came up with this idea over coffee one afternoon and worked on the lyrics together. The next thing I know, a producer's ringing me up to say congratulations for getting my song on Robbie's record. I didn't know what he was talking about!"I was shocked. When you work with someone, you're legally entitled to a share of the publishing. I have demos of the tape and will see him in court if I have to. I just want him to be a man and do the right thing."
Ashley claims Robbie went "ballistic" when he tried to approach him and threatened to remove the track from his new album 'Rudebox'.