Five Labour supporters have abandoned their attempt to overturn a court ruling which has barred 130,000 new members from voting in the party's upcoming leadership contest.
The group said it would cost £1,000 to get their case heard by the Supreme Court - on top of the more than £80,000 in legal fees and costs they have already had to pay.
Last Monday, the five campaigners had won a High Court battle against Labour's ruling body, paving the way for all members who joined after 12 January to vote in next month's election between Jeremy Corbyn and Owen Smith.
But days later, the Court of Appeal overturned that judgment - backing the National Executive Committee's decision to only afford a ballot paper to members who paid a £25 fee over a special 48-hour period.
It is thought that many of those 130,000 members would have voted for Mr Corbyn, meaning their exclusion could benefit Mr Smith.
Lawyers for the five - Christine Evangelou, Hannah Fordham, Chris Granger, Rev Edward Leir and an unnamed teenager - had argued the NEC had no power to retrospectively freeze voting rights.
The Supreme Court was reportedly making urgent arrangements to interrupt its summer recess so five justices could hear the case.
In a message posted on the crowdfunding website where the group had raised more than £93,000 to put towards legal fees, Ms Fordham said: "This has been an odd, emotional rollercoaster of a week for us all.
"Thank you for supporting us through this, it's been a huge help to see how many of you care deeply about this unfair and unjust situation."
She said that their case was not in vain, as although votes for all "disenfranchised" members were not reclaimed, the challenge had sparked important conversations about the NEC's role.
A spokesman for Mr Corbyn's campaign praised the group's efforts, adding: "The strength of solidarity shown to the five claimants campaigning for the democratic rights of their fellow Labour Party members has been truly remarkable."
Mr Corbyn appears to be in high spirits and optimistic of a Labour government after the next election.
With over 500,000 members, Labour can be at the heart of every community in Britain & win the next General Election pic.twitter.com/ojOvRTowmV
— Jeremy Corbyn MP (@jeremycorbyn) August 13, 2016