A Brexit campaigner fined £20,000 for breaking EU referendum spending laws is raising cash online to fund a court appeal against the judgement.
BeLeave founder Darren Grimes says he is "completely innocent" of making false declarations in relation to a £680,000 donation from Vote Leave.
He accused the Electoral Commission of "bias" against Leave supporters and has already raised more than £27,000.
The watchdog insisted its investigation was "thorough and fair".
It said it had carried out inquiries into campaigners on both sides of the referendum battle.
Mr Grimes said the online donations will go directly to his lawyer to mount a legal challenge and not to pay his fine.
Last week, Brexit campaign group Vote Leave was fined £61,000 after an Electoral Commission investigation found it broke electoral law.
The watchdog said it exceeded its £7m spending limit by funnelling £675,315 through the youth group BeLeave, set up by Mr Grimes when he was a fashion student at Brighton university.
It also found the donation should have been declared as part of Vote Leave's spending, because the two groups were working jointly.
The watchdog said the cash was spent with Canadian data firm Aggregate IQ, which had been working for Vote Leave to create highly targeted social media ads, in a "common plan" between the official campaign and Mr Grimes's group.
Mr Grimes, 24, was fined and referred to the police in relation to false declarations of campaign spending, along with Vote Leave official David Halsall.
Vote Leave - the official Leave campaign fronted by leading politicians including Boris Johnson and Michael Gove in the 2016 referendum - said the "wholly inaccurate" report was politically motivated.
In a statement, Mr Grimes insisted the commission's judgement was "simply wrong and based on inaccurate assertions and a misunderstanding of the law".
He said he was "just the latest in a long line of Leave campaigners that the commission have issued trumped-up charges against".
"I am not a rich person. I honestly don't know how I'm going to pay the maximum fine that they've unfairly slapped me with - despite saying there are 'substantial' matters in mitigation that they've decided to ignore," he said.
"But this isn't just about me. Most importantly, I don't want to let the commission get away with this."
He said the commission's conduct had been "appalling" and its judgement against him a "result of bias".
"I think they are undermining our democracy, and I am asking for help to expose what they are doing and to stop them," he said.
Less than two hours after announcing his appeal, Mr Grimes had received pledges of more than £27,000.
The Electoral Commission - which is the watchdog overseeing elections in the UK and ensuring that UK laws on spending by political parties are followed - said it had applied its sanctions accordingly after a "thorough and fair investigation".
"The laws we enforce were put in place by Parliament to provide voters with transparency and confidence in the system," it said.
"We open investigations where the evidence justifies it, irrespective of the political views of the party or campaigner concerned."
The commission said between June 2016 and April 2018 it had published details of 38 investigations arising from the EU referendum, where offences were found - including Remain and Leave campaigners.
The result of the referendum was 51.9% for Leave and 48.1% for Remain. The UK is due to officially leave the European Union at 23:00 GMT on 29 March, 2019.