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Rex Features
In court papers Ono claims that Murphy is exploiting the name and "fraudulently" registered it as a trademark.
Murphy registered the stagename in 2003 after consulting with Ono. The widow of former Beatle Lennon had no complaint at the time but now claims the use is "tarnishment" towards her late husband.
Posting to fans on her MySpace blog, Murphy said: "This could very well mean the career that I have worked so hard at, the one you all have believed in, may come to an end."
The singer added: "If Yoko prevails, Lennon might never be able to tour or release records using the name Lennon."
Julian Lennon, John's son, does not have a problem with Murphy using his father's name.
"She has my full support," he wrote on his MySpace page.
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