(Bloomberg) — Democratic lawmakers, with President Joe Biden’s support, are drawing up details of a plan to tax billionaires and other ultra-high earners after Senator Kyrsten Sinema’s opposition to raising the rate on corporations sank a key funding component for a multitrillion-dollar social-spending package.

His office says that Ron Wyden is the Oregon Democrat who chairs the Senate Finance Committee. He plans to introduce a new tax to tax the capital gains unrealized by the ultra-rich next week. The proposal, which has support from other Democratic lawmakers, would set the so-called billionaires’ income tax at $1 billion in assets, or three consecutive years of $100 million or more in income — hitting some 700 taxpayers.

This tax could be applied to many items, including stocks, bonds and real estate. Gains in value would also be taxed annually, regardless of the sale or purchase of an asset. A version of the proposal that dates back to 2019 suggests that annual value decreases could be also deducted.

Wyden promoted this plan as part of an ongoing effort to tax capital in the same way that income is taxed. Sinema’s opposition to corporate and individual tax-rate increases might give the unorthodox tax increased leverage in the drafting process, because it could raise significant amounts of revenue for the social-spending package Democrats want to advance without her needing to change her position.

Biden has signaled support for Wyden’s idea, though the complex new tax regime has yet to receive full vetting among Senate Democrats. It also has support from progressive senators Elizabeth Warren of Massachusetts — who for years has promoted a wealth tax — and Ohio’s Sherrod Brown, members of Wyden’s tax policy committee.

More: Biden searches for cash to fund his agenda after a setback on tax rates

“If you don’t want to pay any taxes in America, what you do is you buy, you borrow, and you die,” Wyden said earlier this month. “Those three things get out of paying taxes and nurses and firefighters pay taxes every year, and under my plan, billionaires will, too.”

Some of the plan’s details were reported earlier by the Washington Post.

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Biden acknowledged Thursday that he doesn’t have sufficient Senate Democratic backing for his proposed increase in the U.S. corporate tax rate giving fresh impetus to efforts by negotiators to find alternative revenue sources for their sweeping social-spending bill. Nearly all of the options, including the billionaires’ tax, are more complicated and politically risky than just increasing the top-line rate.

Biden had sought to boost the 21% corporate tax rate, which had been lowered to that level in President Donald Trump’s signature tax overhaul. But at a CNN town hall on Thursday night Biden said, “I don’t think we’re going to be able to get the vote,” speaking in response to a question.

Sinema’s press secretary, Hannah Hurley, said Friday that the senator, an Arizona Democrat, would “continue to work directly in good faith with the White House, Senate leadership, and her colleagues to expand economic opportunity while growing American economic competitiveness.”

“She has told her colleagues and the president that simply raising tax rates will not in any way address the challenge of tax avoidance or improve economic competitiveness,” Hurley added.

The new tax is among several ideas Wyden has pushed as his “menu of options” to pay for the social spending package, many of which are tax changes that may not violate Sinema’s opposition to increasing taxes on corporations and individuals earning more than $400,000, as the White House and other Democrats want to do. Democrats have to decide which “revenue-raisers” they are comfortable with.

Wyden’s counterpart in the House of Representatives, Ways and Means Committee Chairman Richard Neal, a Massachusetts Democrat, has expressed concern about introducing new tax concepts as a way to pay for direct spending programs Democrats want, instead of simpler rate increases.

“I don’t want to rule anything out but I think that it is very late in the business,” Neal told reporters Thursday. “It is the ninth inning.”

Neal added that he’s concerned about how items that don’t have public market prices, like real estate and art, might be taxed. Sinema was also on his mind to convince her about the rate hikes for individuals and corporations that he had recommended to his committee.  “I made my case for the rates in term of efficiency, simplicity, and they weren’t punitive,” he said.

According to a summary obtained from Wyden’s office, taxes for nontradable assets like real estate or stakes in businesses would be calculated on an annual basis, but the taxes plus interest would be payable upon sale of the asset. It is possible to pay interest and tax over time as opposed to all at once. Tradable assets are treated as if they were being sold at fair value.

Wyden hopes the new tax will generate hundreds of billions of dollars to pay for social spending programs. Wyden estimates that 700 taxpayers would have to pay the new tax. Although not a wealth tax in the official sense, Wyden believes that there is enough support to raise taxes on the rich and create momentum for a new kind of levy.

In story published Oct. 22, corrections to second paragraph. This is $1 billion worth of assets. Not annual income. Makes distinction in deck headline.

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