Members of UB40 have said they were seeking legal advice after three former bandmates began using the same name, which they dismissed as a desperate attempt to "hijack" the group's legacy.
The members who had retained their name kept silent about the move until today but today said it was a "pathetic" attempt to " confuse and manipulate" fans.
A statement issued by five remaining founder members Brian Travers, Jimmy Brown, Earl Falconer, Norman Hassan and Ali's brother Robin Campbell said they were now consulting lawyers.
It said: " We are outraged at this latest desperate attempt by our former band mates to hijack UB40's brand name, business and legacy. As UB40 we have worked continuously for the last 35 years touring the world with our live show and promoting our recorded albums.
"As our fans know, Ali Campbell left UB40 six years ago citing issues with the band's management, and has since pursued a solo career.
"In that time, Ali has repeatedly attempted to discredit his brothers and former band mates, through the media and otherwise, but this latest attempt to confuse and manipulate UB40's fans is, frankly, pathetic. We are disappointed that he feels it necessary to behave in this way and equally disappointed that Astro has joined with him."
Trumpeter and vocalist Astro walked out on the group late last year and immediately hooked up with Ali.
The statement went on: " As for Ali, Mickey and Astro, the matter is now in the hands of our lawyers".
The group clocked up a string of hits with songs such as Food For Thought, One In Ten and Red Red Wine.
A spokesman for the breakaway trio last week threw down the gauntlet by announcing "the three founding members (were) back together, performing and recording as UB40 once more".
The existence of two groups sharing the same name echoes other disputes over the years including a legal battle for the right to the name Bucks Fizz. In the court fight which three past members of the Eurovision-winning group brought against the sole original member who had retained the rights to the name, they were judged to have given up their rights by leaving the line-up.
The musicians may not have the stomach for a lengthy legal fight as several - sax player Travers, drummer Brown, percussionist Hassan and Astro - were made bankrupt in 2011. Their financial difficulties had been ongoing for a number of years.