AceShowbiz -

Jimmy Page, John Paul Jones, and Jason Bonham reportedly give their frontman Robert Plant an ultimatum, saying that if he refuses to re-join Led Zeppelin on their comeback tour, he will then be replaced by a new singer. "They will be finalizing plans for shows over the next couple of months and will tell Robert that if he doesn't want to be involved they will go ahead without him," a source says.

Speaking of the possible reunion, the source reveals that the three members of the band "are determined a tour will go ahead next year" and there's an American guy who has been standing in for Robert regularly and doing a great job. The source close to the band states, "They've been rehearsing frequently in London and the band is really gelling."

Furthermore, some claim that Robert's reluctance to re-join the band happens because he has worked on a side project with country singer Alison Krauss. Their duet on an album called "Raising Sand" has been honored as Album of the Year at Americana Music Association's 7th Annual Honors & Awards show at Nashville's Ryman Auditorium on September 18.

Previously, Robert admitted that huge amounts of paperwork from the record industry bureaucracy have put him off the idea of the band's comeback plan. Despite the band's last year's success at London's O2 arena, the rocker explains that just for the O2 show, they have to deal with "endless paperwork" that stressed them out. "I'm thinking of compiling them for a book, which I feel sure would be hailed as a sort of literary version of Spinal Tap," he adds.