Wealth tax proposals pushed by two leading Democratic presidential candidates would cost American workers more than $1 trillion, according to a study released by a conservative economist on Friday in a possible preview of Republican attacks against the idea.

The wealth tax plans would raise trillions of dollars in new federal revenue but would lead to lower pay by depleting business investment and, therefore, worker productivity, said Douglas Holtz-Eakin, who has served as director of the Congressional Budget Office and an adviser for numerous Republican politicians, including President George H.W. Bush.

The wealth tax has emerged as a defining issue in the 2020 Democratic presidential campaign, as Sens. Bernie Sanders (I-Vt.) and Elizabeth Warren (D-Mass.) have called for using versions of it to fund large new government programs. Some of the tax proposals have elicited outrage from the wealthiest Americans, but supporters say the proposals are meant to address record levels of income inequality that continue to worsen.

Conservatives have primarily criticized the wealth tax ideas as confiscatory and impractical, but the new paper makes the claim it could have more far-reaching consequences in the American economy.

“The tax constitutes a reduction in the supply of capital, and as a result it will reduce investment in innovation, lower productivity growth, and thus reduce wage growth,” said Holtz-Eakin, now president of the American Action Forum, a conservative organization.

Several economists disputed Holtz-Eakin’s findings, arguing he overstates, among other things, the wealth tax’s impact on business investment. Only a small fraction of the top 1 percent would be wealthy enough to pay the tax. And business investment has fallen in the past year after the Trump administration cut taxes, muddying assumptions over how changes in tax policy spur new investment.

The paper also ignores the widespread benefits of the new programs the tax could fund for growth and productivity, critics said.

“Does anyone still believe stock market bubbles, real estate bubbles and other asset price bubbles are ‘productive’? ” said Robert Hockett, a policy expert at Cornell University who has advised Warren and Sanders on economic policy matters. Hockett said the analysis “seems to be calculated more to impressing nonexperts than to actually deriving plausible forecasts.”

Taxes on capital have already been cut dramatically since the middle of the last century but have corresponded with a decrease in investment and savings, rather than an increase, said Matt Bruenig, founder of the left-leaning People’s Policy Project.

Warren’s original pitch called for levying a 2 percent tax on wealth above $50 million, as well as a 3 percent tax on wealth above $1 billion. She later expanded the scope of her wealth tax to 6 percent on wealth above $1 billion, to help finance her proposal for a Medicare-for-all single-payer health-care system.

Sanders would hit more people with the tax and would also significantly increase how much it would affect the very wealthiest. His plan introduces a new 1 percent wealth tax on those earning over $32 million, then increases that rate in steps until it reaches 8 percent for those with more than $10 billion.

The initial wealth tax raised by Warren would raise close to $3 trillion over 10 years — enough money to fund universal child care, make public colleges and universities tuition-free, and forgive a majority of the student debt held in the United States, according to some nonpartisan estimates.

Sanders’s wealth tax would raise more than $4 trillion over 10 years, according to Holtz-Eakin, although he also says the amount raised from the plan would dwindle substantially in the long run. Sanders has proposed using that money to fund programs such as Medicare-for-all and a Green New Deal, a massive set of federal investments aimed at combating climate change.

The wealth tax proposals would represent a sweeping transformation of how taxes are assessed in the United States, shifting from more traditional Democratic tax plans that target new sources of income.

Inequality has risen rapidly in the United States in recent decades, with the 400 richest Americans’ share of the national wealth tripling since the early 1980s, according to estimates by left-leaning economists.

Holtz-Eakin also found the wealth tax would reduce overall economic growth by $1.3 trillion and investment levels by a similar amount.