Ms Reeves has recently indicated that a wealth tax has been ruled out but tougher regimes for capital gains tax and inheritance tax remain likely.
The Chancellor is said to be looking at reforming inheritance tax reliefs offered for businesses and agriculture, which grant 50pc relief on the value of property and land.
Shares of companies on the junior Aim stock market for growth businesses are also eligible for tax relief.
Such exclusions were designed to prevent a death leading to the break-up of farms and other businesses, but Labour believes they have been exploited by the wealthy putting their money into property and share portfolios to avoid inheritance tax.
However, the problem for Ms Reeves is that while the system clearly favours the better-off, changing it will destabilise investment markets.
Mr Hollands said: “Removing eligibility for business relief in a clunky way from Aim would be hugely damaging to the exchange and deny SMEs an important source of funding.
“Estimates vary on how much of Aim is owned by investors seeking business relief, but services explicitly billed as inheritance tax mitigation strategies own at least 10pc of the market and then there are also investors doing this themselves.
“I would hazard a guess that around 15pc to 20pc of Aim is owned by investors seeking this relief.
“Aim has been struggling for some time from a dearth of IPOs and a shrinkage in the number of companies on it, so removing business relief would be a real hammer blow, especially if there were no transitional arrangements that would deter existing shareholders from selling.”
Other measures being looked at by the Chancellor include increases in employer National Insurance contributions, changes to pension allowances and a rise in fuel duty.
A report by accounting and business advisory firm BDO, published on Monday, found many of the 500 mid-sized businesses surveyed were concerned about the impact of the Budget.
Richard Austin, partner at BDO said: “These businesses are crying out for some certainty.”
A Treasury spokesman said: “The Chancellor has vowed to lead the most pro-growth government in Britain’s history, restoring economic stability and delivering more investment into the UK economy.
“The record-breaking £63bn of private investment secured at the International Investment Summit is a vote of confidence that shows the UK is one of the best places in the world to do business, building on reforms to our broken planning system and support for businesses through capping corporation tax at 25pc and publishing a business tax roadmap to deliver the certainty they need to plan for the future.”