Roy Morgan Research's monthly business confidence index fell 9.1 per cent in May, down from 123.1 to 111.9.
A statement by the research house said the "large drop" in business confidence is likely to be more tied to the "poorly received" federal budget than "uncertainty surrounding the upcoming federal election".
"The level of business confidence in May is clearly negative for the economy overall, and now below the year average (116.7)," said Roy Morgan.
"The weakest indicators in May relate to the upcoming year, which suggests the impact of election uncertainty.
"Net expectations of business performance over the next 12 months have dropped to 20.6 points (down 17.5 points in May) and net views of whether the next 12 months will be a ‘good/bad time to invest’ are now 12.1 points (down 14.2 points)," said Roy Morgan.
Roy Morgan industry communications director Norman Morris said the "worst possible outcome" of a federal election for business confidence – a hung Parliament – is currently "looming large".
"Unfortunately for businesses, the longest federal election campaign for more than 60 years ensures there will be little clarity on this issue until July – at the earliest," Mr Morris said.
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