Sydney-based designer Katie Jane Taylor - nee Katie Perry - is suing the American singer-songwriter over the sale of Katy Perry-branded clothing in Australia at concerts, in department stores and a range of online stores.

Ms Taylor continues to trade under her birth name, which she trademarked for clothing in 2008.

That's the same year the pop star - legally known as Katheryn Elizabeth Hudson - shot to worldwide fame with the 2008 hit I Kissed A Girl.

Ms Hudson, whose stage name combines her first name and her mother's maiden name, is defending the allegation of trademark infringement and has launched a cross-claim to have Ms Taylor's trademark cancelled.

She has pleaded that she uses the Katy Perry name in good faith and her use on clothing is unlikely to deceive or cause confusion.

Justice Brigitte Markovic is due to hear the case over five days, beginning on Monday.

Ms Taylor is due to testify on Tuesday.

The US-based pop star is not expected to give evidence.

"This is a real David and Goliath fight,'" Ms Taylor said in a statement on Friday.

"I am fighting not just for myself, but for all small businesses in this country who can be bullied by these overseas entities who have much more financial power than we do."

Her case is funded by global litigation funder LCM.