The minimum tax, sometimes called the book income tax, is part of the Build Back Better bill that the House passed last month. It’s supposed to raise $319 billion in revenue over 10 years.

It also adds complexity to an already byzantine tax code and gives companies less incentive to invest in new equipment. Critics fear that it will politicize the world of corporate accounting.

When you read that Amazon, for example, paid just 4.3% of its profits in federal income tax over the last three years, it’s important to understand that the profits and the tax liability are calculated under different sets of rules.

If Amazon buys a computer server, standard corporate accounting depreciates the asset over its useful life, which might be seven years. Only 14% of the server’s cost would count against this year’s profit.

For tax purposes, though, companies since 2017 have been allowed to immediately deduct 100% of certain capital expenses. If a company spends heavily on capital equipment, that brings its effective tax rate well below the statutory rate of 21%.

Michele Meckfessel, an assistant professor of accounting at the University of Missouri St. Louis, said depreciation accounts for the biggest part of the gap between taxable income and the profit companies report to shareholders. Tax-loss carryforwards are another big difference-maker for companies like Amazon, which lost money for years before coming profitable.

Congress created each tax break for a reason. Bonus depreciation is supposed to give companies more incentive to buy new trucks, computers and machinery.

Only about 300 companies will be subject to the minimum tax, but Thornton Matheson, senior fellow at the Tax Policy Center, estimates that they account for 60% of capital spending. Effective tax rates will rise sharply for companies in capital-intensive industries like utilities, transportation, manufacturing and construction.

If those companies respond by trimming their capital budgets, she said, the new policy will hurt the economy.

“What this book minimum tax really addresses is the political awkwardness of very large corporations paying a minimal amount of tax,” Matheson said. “It would be preferable, and less complicated, to reform the corporate tax itself.”

Garrett Watson, senior policy analyst at the Tax Foundation, also thinks the minimum tax is the wrong way to achieve fairness. “A better option would be to directly change the tax code if there’s a reason to think some of the tax breaks are too generous,” he said.

Basing part of the tax code on financial-statement accounting may cause other problems. Instead of showing investors an accurate picture of their business, corporate executives may feel pressure to report lower profits and minimize their tax burden. The Financial Accounting Standards Board might feel pressure to write accounting rules that raise government revenue.

Meckfessel believes those are real dangers. “There are already enough incentives in place for executives to obfuscate, and if you tie book profits to taxation, you have even greater incentive to misrepresent what’s going on,” she said.

Financial accounting is all about providing clear information to investors. The tax code is about raising revenue for the government, while pursuing social goals like encouraging certain types of investment.

Accurate reporting and efficient taxation aren’t incompatible goals, but they require different sets of rules. If we start to mix up the rules, we’re likely to fall short of both objectives.