The Bristol Pound currency is set to end in March unless £100,000 is found to keep it running, the organisation in charge has said.
Bristol Pound launched seven years ago but since then, cashless payments and cryptocurrencies have grown in popularity, making it less competitive.
Managing director Diana Finch said they only had £65,000 left to pay for the £13,000 monthly running costs.
Bristol Pounds £B would revert to sterling if the scheme folds.
Ms Finch said: "There are ongoing costs just to maintain the current infrastructure, and that costs about £13,000 a month just to keep the show on the road, so that's why we are ringing the alarm bells now."
There is £400,000 in digital form and £35,000 in vouchers in circulation.
The vouchers are valid until September 2021.
"All of the digital money that people hold is in accounts at the Bristol Credit Union (BCU) which would just revert to sterling if we stop running the digital scheme.
"The paper money is backed completely separately outside our accounts, in a trust account, again at the BCU, so it's very safe" she said.
The organisation has said despite its likely demise, the goal was still to encourage people to rethink their spending habits and their impact on the environment.
"The aims of the currency are to create a greener, fairer economy for Bristol.
"Day by day we are seeing terrible headlines about the climate emergency and the level of CO2 emissions is still increasing - and this is being fuelled by people buying more stuff, and more stuff than the Earth can produce.
"We need to localise our economy, we need to reduce our consumption and we need to think about the provenance of every single thing we spend our money on," added Ms Finch.
She added that the organisation was bidding for government funding to create a digital platform where customers could earn reward points by choosing local goods and services.