Angela Eagle has urged Labour supporters to "save" the party, and "heal" the country by signing up to remove leader Jeremy Corbyn.
Ms Eagle has pleaded with opponents of Mr Corbyn to pay the increased £25 fee to challenge his leadership.
Speaking to the BBC, she said: "I would say to the nine million Labour voters out there, there's two days next week when you can actually pay £25, help save the Labour Party, make our democracy work and help me heal our country. Join as a registered supporter.
"Join us in this battle, let us win the Labour Party back", she added.
Ms Eagle also said the membership fee was "pretty good investment for the whole future of democracy".
The shadow chancellor earned loud cheers as he launched an foul-mouthed attack on the MPs seeking to replace his friend Corbyn.
The MP for Pontypridd resigned as shadow work and pensions secretary last month in protest at Jeremy Corbyn's leadership.
I now realise that my earlier description of the NEC meeting - as an omni-shambles - was generous.