Victor Shields, director of VMS Enterprises, was forced to take the party – since rebranded and led by Richard Tice – to court over the bill from the 2019 general election.
Despite Glasgow Sheriff Court agreeing the party should pay up, it has consistently refused to answer letters or pay the sum owed to the businessman, forcing him to take further legal action in England.
It is understood a winding up petition was served on the political party last week, with a hearing set for September 7 or soon thereafter.
Reform UK has consistently rejected the claim, now worth more than £26,000 after interest and before court expenses are taken into account.
A winding up order, if granted by the court, would see the party face liquidation proceedings to pay the outstanding amount and could include an investigation into director conduct.
The initial Scottish court case arose after a dispute between the party and VMS Enterprises around payment for election billboards in London during the general election campaign.
The court stated the party was liable for the bill for advertising services after some invoices were paid by Brexit Party staff and others were not questioned.
Several invoices had gone unpaid amid claims a volunteer did not have the authority to charge the party for the billboards.
However, the court stated the failure to question the payment of invoices incurred by candidates meant the party was liable for the full costs.
Speaking to The Scotsman last year, Mr Shields attacked Reform UK’s “hypocrisy” in failing to pay.
He said: “I was quite happy to keep quiet after the judgment because I assumed they would respect the Scottish courts and duly pay us.
"They don't care. They feel they are above the law.
"Richard Tice is positioning himself to the right of Boris [Johnson] and trying to capture the Conservative voters, Scottish voters too and here we are being forced to go to English courts, for me being forced to spend further money, to try and recover a debt that is legally due to us."
The court case heard witnesses describe the organisation of the Brexit Party, then led by former UKIP leader Nigel Farage, as "shambolic" by a party official as it struggled to cope with its popularity and decision to pull hundreds of candidates from the ballot paper ahead of polling day.
Witnesses told the court the party’s organisational structure "visibly started to fall apart", was "very unprofessional" and "beyond chaotic" ahead of the 2019 election.
Reform UK’s latest accounts state that in 2020 it received nearly £3 million in donations, with a further £17m in 2019.
Reform UK has been contacted for comment by The Scotsman.