A spokeswoman for Justin Bieber has denied claims that the 17-year-old has become a father.
A 20-year-old woman has reportedly told a US magazine that the teenage singer is the father of her three-month-old boy.
Star magazine has pictured Mariah Yeater on its front cover holding her son.
It says she has hired lawyers to seek financial support and a paternity test.
Justin Bieber's management say: "While we haven't yet seen the lawsuit, it's sad that someone would fabricate, malicious, defamatory and demonstrably false claims.
"We will vigorously pursue all available legal remedies to defend and protect Justin against these allegations."
According to the magazine, Mariah Yeater claims the pair met backstage at a concert when Bieber was 16.
On his Twitter feed, Bieber wrote: "So I'm going to ignore the rumours and focus on what is real. An opportunity to help by doing what I love. Judge me on the music!"
Justin is performing at the MTV Europe Music Awards in Belfast on Sunday 6 November.
He's also due to turn on the Christmas lights at two shopping centres in London next week.