The warning comes as a survey of trading standards officers reveal widespread concern that consumers will fall victim to illegal - and legal - loan companies as they struggle to make ends meet in a difficult economic climate.
A massive 15% of the trading standards workforce has already been slashed under the coalition government, with huge reductions to activities across the board.
The union said these cuts were reducing the ability of the remaining workforce not only to identify and crack down on loan sharks, but also to educate the public on the risks of loan companies before they end up in debt.
The new survey, carried out as part of The Damage, the union's far-reaching investigation into the impact of public service budget cuts, revealed that almost 85% of respondents said the public are more likely to turn to unscrupulous money lenders in hard times.
Helga Pile, UNISON national officer for trading standards, said:
"Our members in trading standards are doing their best in increasingly difficult circumstances to stop rogue traders, payday loan companies and sharks from taking the public for a ride, but these services are unsustainable without investment.
"Illegal - and legal - money lenders always flourish in difficult economic times, but staff shortages and budget cuts are holding trading standards services back, allowing these operations to continue preying on the public.
"The irony is that a properly funded and efficient trading standards service actually benefits the economy, returning an average of six pounds for every pound invested, while protecting the interests of legitimate businesses and keeping the public safe."
UNISON is warning the public against finding themselves in debt with unregulated, illegal outfits such as loan sharks, or payday loan companies who often have enormous and complicated rates of interest. Credit unions and mutuals were a safer, legal alternative, the union added.
Trading standards officers' responses to the survey included:
"Consumers may be tempted to use the pay day loans that seem to advertise everywhere - whilst just legal, the interest repayments are extraordinary"
"There are a lot of scams now where people in less affluent areas are cold called on the phone with offers of loans. These loans are non- existent, but the residents don't know this. They have to pay money up front for the release of the funds but the funds are never released and the residents end up paying out more and more money, when they can't afford it."
"Education work has ceased. We have much less ability to raise awareness of loan sharks."
