One Direction are facing legal action over their name from a US band who claim to have been using the same title for almost a year longer.
The Californian quintet have filed a lawsuit after they say their efforts to "negotiate a reasonable compromise" failed.
And they accused the X Factor group's representatives of escalating the dispute by attempting to make them abandon their name.
It comes as the UK group - Harry Styles, Niall Horan, Zayn Malik, Liam Payne and Louis Tomlinson - are taking the American charts by storm.
The US band, formed in 2009, said they liked the Brit act but added: "To protect our rights, we reluctantly have filed a lawsuit."
In their legal action, the Californian group are aiming to stop Simon Cowell's company Syco Entertainment and record company Sony from using the name and are asking for a share of the British act's profits.
In an online message to their fans, they explained: "Despite our best efforts, we were unable to negotiate a reasonable compromise with the handlers for the band."
The group - now on their second album - say they have the rights to the trademark "One Direction" in the US, and said their rivals had known about their claim to the name since the spring of 2011.
"They chose not to use a different name. They chose to press ahead, using the exact same name, One Direction, setting up the current difficulties and confusion in the United States," the US act said in their blog.
And they added that lawyers for the UK group had appeared before the US Patent and Trademark Office to challenge the longer-established band's right to the name.