The impact will be “life-changing” for owners, said Andrew Evans, a tax partner at law firm Geldards.
“I spoke to one client who had saved up £15m to grow their business in a different direction,” he said.
“They’ve decided as a result of these changes they can’t be bothered.”
Mr Evans warned that many owners are unaware of the implications, describing an “ostrich mentality” among small and medium-sized firms.
He urged business owners to seek advice and make a will.
The Treasury has said the changes could raise £520m a year, but Mr Evans questioned whether that was worth the potential impact on growth, adding: “Rather than spend money growing the business, owners will save money to pay a tax bill.
“Personally, I think that’s disappointing and doesn’t accord with the chancellor’s pronouncements she’s in favour of growth.”
A spokesperson for HM Treasury said: “We are a pro-business government that has capped corporation tax at 25%, the lowest rate in the G7, we’re reforming business rates [in England], have secured trade deals with the US, EU and India, and have seen interest rates cut five times since the election, benefiting businesses in every part of Britain.
“Right now, 53% of Business Property Relief – worth £533m – goes to just 158 estates.
“Our reforms will channel that funding into vital public services.”