A top U.S. economist and former Biden official is speaking out after he says he was shocked to find that the Trump administration cited his research in formulating last week’s extreme global tariffs, which he said they got “all wrong.”

University of Chicago economics professor Brent Neiman, who worked for the U.S. Treasury Department under President Joe Biden, wrote in a New York Times op-ed Monday that Trump’s tariffs are roughly four times higher than they should be if they followed his math correctly.

“How on earth did it calculate such huge rates?” he recalled as his immediate shock and confusion upon seeing the numbers unveiled by President Donald Trump at the White House. He then saw his own published research, which he coauthored in 2021, cited by the Office of the U.S. Trade Representative for part of its methodology.

“But it got it wrong. Very wrong,” Neiman wrote. “I disagree fundamentally with the government’s trade policy and approach. But even taking it at face value, our findings suggest the calculated tariffs should be dramatically smaller — perhaps one-fourth as large.”

Other economists have similarly mocked the Trump administration’s tariff formula, calling it “embarrassing” and “malpractice.”

Neiman went on to break down Trump’s policy, including how ― as other economists and world leaders have pointed out ― the tariffs are not reciprocal as Trump claims because reciprocal tariffs “are supposed to treat other countries the way they treat us, and foreign tariffs on American goods are nowhere near these levels.”

He also argued that a simple tit-for-tat tariff system, like the one Trump has proposed, mistakenly assumes that “a tariff placed on one country won’t affect imports from any others and ignores any implications for exports.”

“These assumptions may work for an action against one small trade partner, but not for the broad salvo announced last week,” he wrote.

Beyond the misunderstanding of how global trading and tariffs work, he went on to say that the tariff formula used by the government to calculate its rates is further flawed because it uses four different numbers, which appear based on flawed assumptions.

“The part that directly relates to our research is an estimate of how much import prices change in response to the additional costs imposed by tariffs,” he wrote. “The value of that term, known as the rate of pass-through, isn’t obvious and depends on how companies behave.”

He then questioned where a plugged-in rate of 25% came from, while noting that the Trump administration offers “shockingly few details” in its methodology.

“I would strongly prefer that the policy and methodology be scrapped entirely. But barring that, the administration should divide its results by four,” he concluded.

Neiman, speaking with ABC 7 Chicago, said he has not spoken with the Trump administration directly but that he’s been told they are aware of him pointing out their mistakes.

Despite pushback and criticism, the Trump administration has vowed to stand by its tariffs.

The White House has said that more than 50 countries have since reached out to negotiate a deal. There have been conflicting messages on whether the tariffs can be negotiated, however.

White House trade and manufacturing adviser Peter Navarro, writing of the tariffs in an op-ed Monday, said that “this is not a negotiation.” His stance follows Treasury Secretary Scott Bessent also saying Monday that the Trump administration would “open negotiations” with Japan.

China has meanwhile vowed to retaliate against the U.S., prompting Trump to threaten to increase China’s tariffs by 50%.