President Trump and his Council of Economic Advisors argue that cutting the corporate tax rate would be a major boon to American workers, in that it would substantially boost their household income. This is, as many economists and journalists have pointed out, wrong.

But there is another issue with the Trump- and GOP-proposed corporate-tax plan that has not drawn as much attention. A major provision of the plan—the full details of which are slated to be revealed on Thursday—fails its most basic claim: that it would “prevent companies from shifting profits to tax havens” and limit “offshoring.” Instead, the way that provision is designed, it would actually incentivize U.S. companies to move their operations overseas and to shift profits to tax havens.

Understanding why that’s the case requires understanding how the corporate-tax system works at the moment. Under the U.S.’s current system—a “worldwide” tax system—American corporations’ profits are taxed at the same rate regardless of whether they are earned domestically or abroad. A key difference between these two types of earnings, though, is that profits made abroad aren’t taxed in the U.S. until they are “repatriated” from a foreign subsidiary to a U.S. parent company. (In most cases, however, companies are already investing those foreign profits in American financial assets; they just can’t be returned to shareholders without triggering a corporate tax.)

The current system gets criticism from both the right and the left. Many progressives argue that by letting companies keep profits overseas indefinitely, the system incentivizes them to shift their activities and profits out of the U.S. and into countries with lower tax rates—especially tax havens. Meanwhile, many conservatives and pro-business interests argue that forcing U.S. multinationals to pay taxes on profits they make overseas (after subtracting the taxes they paid to the foreign country) makes them less competitive in foreign markets. There’s also a conservative argument that the system leads companies to stash money in overseas subsidiaries that they might otherwise bring back and invest in the United States if they didn’t get taxed on their foreign income upon repatriation.

Aware of those criticisms, President Obama suggested reforms in 2012 that sought to find some common ground. First, his plan would have imposed a one-time tax on foreign profits that have never been taxed, with all of the proceeds going toward financing a major infrastructure package. (Trump’s proposal has no such infrastructure provision.) Second, Obama sought to lower corporate rates while at the same time eliminating enough loopholes so that the overall amount of taxes that corporations pay wouldn’t change and the deficit wouldn’t increase. (Under Trump’s plan, the net tax cut to corporations is about $2 trillion over 10 years, according to an estimate from the nonpartisan Tax Policy Center.)

And third, Obama proposed a per-country minimum tax on foreign profits, meaning that there’d be a baseline rate—19 percent was what he put forward—that all companies would be required to pay on foreign profits, even if their operations and earnings were coming from countries with extremely low rates. Thus, if a U.S. company booked profits in a tax haven with a corporate rate of only 5 percent, that company would be taxed that year at a rate of 14 percent by the the U.S. government, for a total rate of 19 percent. The idea was that a per-country minimum tax would make it useless for a company to spend time and money shifting profits to tax havens.

The Trump-GOP plan will also propose a minimum tax rate on foreign income, according to multiple reports. But whereas Obama’s plan (which ultimately didn’t become law) assessed a company’s taxation in each country individually, the Trump framework would come up with an average for all foreign earnings combined, a so-called “global minimum.”

This might seem like a small difference, but the design of their global minimum tax creates perverse incentives for companies to offshore jobs and shift profits to tax havens—outcomes that a per-country minimum tax would avoid. How? Consider two examples, assuming for simplicity that the GOP plan would impose a domestic corporate tax rate of 20 percent (as the Treasury has said it will) and a rate of 10 percent on overseas earnings (it’s expected to be in the range of 10 to 15 percent, but that won’t be known for certain until Thursday). Say there’s a company with two branches that each produce $100 million in profits a year, one in Minneapolis that faces the domestic rate of 20 percent and one in Bermuda, a country that has a corporate tax rate of zero. If the GOP plan used Obama’s per-country-minimum approach, the company would pay $20 million in taxes on its profits in Minneapolis and $10 million on its profits in Bermuda. In total, the company would pay $30 million on $200 million of profits.

This situation changes dramatically if that per-country assessment is replaced by the global minimum in the Trump-GOP plan. All the company has to do to cut its tax bill is move its Minneapolis operation to a country with a corporate tax rate in the neighborhood of what the GOP is proposing, such as the U.K., France, and Germany. That’s because if the company pays $20 million to the U.K. government—instead of to the U.S. government—and still faces no taxes in Bermuda, then it would achieve a 10 percent average on its foreign profits, meaning it would avoid triggering the minimum tax altogether and cut its total tax bill from $30 million to $20 million. On top of this, all of the company’s tax revenues that used to go to the U.S. government now go to the U.K.

This is a big flaw in Trump’s plan: The more an American company moves its profitable operations to countries that have tax rates of 20 percent or higher—often rich countries that are seen as America’s economic competitors—the more that company can shift profits to tax havens without paying taxes on those profits. And the more that U.S. companies already take advantage of tax havens, the bigger the incentive they will have to offshore operations to other advanced countries: This provision of the GOP plan encourages companies to blend income from low-tax countries with that from higher-tax countries, completely avoiding paying money to the U.S. government.

Many economists agree about the problems with this global minimum tax. As Kimberly Clausing, a professor of economics at Reed College who specializes in international taxation, told the Senate Finance Committee in early October, companies would be able to “use taxes paid in Germany to offset the Bermuda income and then you have an incentive to move income to both Bermuda and Germany.” Similarly, Ed Kleinbard, a law professor at USC and a former chief of staff of Congress’s Joint Committee on Taxation, told Bloomberg, “Companies will double down on tax-planning technologies to create a stream of zero-tax income that brings their average down to that minimum rate.”

Why would Trump and Republicans in Congress support a plan designed to incentivize sending jobs overseas and transferring tax revenues from the U.S. to other countries? The answer is that such a plan would please large multinational companies, who lobbied heavily for a minimum tax on foreign earnings to be watered down. In other words, instead of a minimum tax that would discourage companies from moving jobs and shifting profits overseas, Trump and congressional Republicans have settled on one that would encourage more of both.