The proposed measure calls for higher taxes for individuals and countries from countries whose tax policies are deemed by the US to be discriminatory. This could affect foreign investors, further adding to concerns at how US assets are seen abroad.

An “obscure” tax measure contained within President Donald Trump’s tax and spending bill going through Congress is rattling Wall Street, Bloomberg reported late last week.

The item – introduced in legislation that was passed in the House as Section 899 and titled “Enforcement of Remedies Against Unfair Foreign Taxes” – calls for, among other things, increasing tax rates for individuals and companies from countries whose tax policies the US deems “discriminatory,” the article said.

This includes raising tax rates on passive income, such as interest and dividends, earned by investors who are potentially sitting on trillions in the US.

The measure, if it becomes law, would further alienate foreign investors, the report said.

The report quoted Michael Brown, a strategist at Pepperstone Group, a brokerage firm founded in Melbourne, Australia, whose clients are all outside the US, as saying: “We’re already dealing with a market where Treasuries, to foreign investors, probably aren’t the most attractive investment. If you’re now talking about massively unfavourable tax treatment, then it’s just another reason to stay away.”

The report said that among those potentially affected are institutional investors including sovereign wealth funds, pension funds and even government entities, as well as retail investors and businesses with US assets.