Many self-employed people set up limited companies and receive payments through dividends, rather than a salary.
It has also become a popular way for investors to receive income from buy-to-let properties amid the erosion of landlord tax perks.
Dividend taxes were hiked for all income taxpayers in 2016, while the 10% dividend tax credit was scrapped and replaced with a tax-free allowance.
One broker told Mortgage Solutions the changes had tripled his tax bill.
Earlier this year, the chancellor Philip Hammond announced a fresh crackdown, by cutting the dividend allowance from £5,000 to £2,000 in April 2018.
Dividend tax starts at 7.5% for basic rate taxpayers and jumps to 32.5% for higher rate taxpayers.
The reduction in the allowance will increase tax bills by around £1,000 for higher rate taxpayers, according to analysis.
Chancellor could again target dividends
But owners of limited companies could be set for further tax rises, as the cash-strapped chancellor looks to fund giveaways, such as stamp duty cuts in the Autumn Budget.
Danny Cox chartered financial planner at Hargreaves Lansdown predicts the dividend allowance could be cut even further below the £2,000 limit or the tax on dividends raised higher.
Chris Sanger, head of tax policy at EY, said: “Whilst we saw a reduction in the dividend allowance in the last Budget, the tax was introduced to offset the benefit of working through a company, but the rate was not increased when the corporation tax rate was reduced.”
Sanger believes the chancellor could take a wider look at workers and reform tax for those who are self-employed.
He added: “We could see more clarification on classes of worker for indirect pay arrangements.
“Will there be some grandfathering of arrangements?
“With a review of modern employment practices already underway, this is an area that looks set to see a fundamental review of its tax and social security treatment.”