The far-right party, which has two MEPs and more than 70 councillors, says the cost of fighting lawsuits has left it "cash struck" and it needs £150,000 to survive.
The BNP is facing legal action from the Equality and Human Rights Commission which won a ruling earlier this year forcing the party to scrap its "whites only" membership rules.
Both sides are due back in court next month after the commission claimed some terms of the court order have not been met.
In an email to supporters, BNP leader Nick Griffin said they should be aware of "a grave situation we find ourselves in".
"The party is now suffering acute legal and financial pressure," he wrote.
"Some of the money we had allocated to pay other pressing bills had to be diverted to this most urgent fight."
"We need to raise £150,000 to keep the wolves at bay and to ensure our survival."
The party's financial problems come after a split which has led to the resignation or suspension of a number of key figures.
The BNP's former legal adviser, Lee Barnes, has claimed in an open resignation letter that the party is in such a poor financial state it could be declared bankrupt.
"As far as I am aware donations to the party have flowed to a trickle as well as party renewals and new inquiries," Mr Barnes wrote.
"Outstanding court costs, wages bills, election expenses and also forthcoming legal cases against the party mean the BNP is now technically bankrupt."
Mr Barnes says the cost of legal action brought by Unilever in April over the use of a picture of a Marmite jar in campaign material is an example of the party "squandering" cash.
"Regardless of how much income the party has had over the last few years, hundreds of thousands of pounds have been squandered on avoidable court cases."
Unilever says it has now settled the case on confidential terms.
The split in the BNP came to a head in April when its then head of publicity, Mark Collett, was arrested on suspicion of making death threats against Mr Griffin.
No charges were brought and Humberside Police have confirmed that Mr Collett faces no further action.
The BNP has not responded to a request for a comment.
Sky News
