The door is slamming shut on a $50 billion tax loophole used by the super-rich

• The US Treasury and IRS are closing a tax loophole used by the uber-wealthy.
• They're cracking down on 'opaque' business structures that 'inflate' deductions. 
• The proposed regulations could generate $50 billion in fresh tax revenues, the agencies said.

The Treasury and IRS proposed new tax regulations Monday targeting the uber-wealthy that they say could result in $50 billion in fresh tax revenues over the next decade.

The initiative seeks to crack down on "related party basis shifting transactions" — or the use of "opaque business structures to inflate tax deductions," according to a Treasury press release.

This occurs, for instance, when a single company operating as different legal entities shifts the tax basis from a property that doesn't generate deductions to one that does, the agency explained.

The practice is contributing to the $160 billion annual tax gap among the top 1% of filers, the Treasury said.

Filings from pass-through businesses with more than $10 million in assets increased 70% from 2010 to 2019, the Treasury said, as audits fell from 3.8% to 0.1% over the same period.

The multi-stage initiative follows a year of research, the Treasury said, and proposes several new rules, including increasing reporting for basis-shifting transactions.

The agencies also issued a revenue ruling stating that certain transactions will be challenged for lacking economic substance.

"Treasury and the IRS are focused on addressing high-end tax abuse from all angles," Treasury Secretary Janet Yellen said in a statement, noting that "resources from President Biden's Inflation Reduction Act" have helped combat "long-standing abuses."

The agencies said they will consider public comments before issuing final rules.