When President Trump announced in February that he was imposing stiff new tariffs on imports from Canada, Mexico, and China, he said his power to do so came from the International Emergency Economic Powers Act, or IEEPA, a law passed by Congress in 1977. Two months later he again invoked that statute as he unveiled his sweeping “Liberation Day” tariffs, which mandated levies of between 10 percent and 50 percent on imports from nearly every country on earth.

When the president subsequently imposed even heavier tariffs on goods from China — the rate on most Chinese imports was ultimately hiked to 145 percent — he once more cited the IEEPA as the source of his authority. And when, to stop the multitrillion-dollar hemorrhaging in financial markets triggered by the global trade war he had launched, Trump suspended some of the tariff increases for 90 days, he relied yet again on the same federal statute.

What a statute it must be! A law that empowers the president to unilaterally overhaul the nation’s tariff schedule, hiking and slashing import taxes and trade duties as he wishes, and subjecting hundreds of millions of people worldwide to his will? There could hardly be a mightier economic weapon in the White House arsenal. Trump plainly has no reservations about aggressively deploying that weapon to vindicate his long-held view that America is being “ripped off by virtually every country we do business with.”

But what about his predecessors? How often did they use the IEEPA to raise and lower tariffs?

Not once.

In the nearly half-century since President Jimmy Carter signed that statute, no president ever invoked it to impose tariffs — not against any country and not for any reason. That wasn’t because seven consecutive presidents failed to make use of a powerful tool granted to them by Congress. It was because no such tool exists.

Trump’s assertions notwithstanding, the International Emergency Economic Powers Act does not authorize presidents to singlehandedly change the tariffs charged on foreign imports. Indeed, nowhere in the 3,700-word statute does the word “tariff” appear. Neither does “duty,” “excise,” “impost,” “levy,” or any other synonym for the taxes charged by governments on imports from other countries. The IEEPA has nothing to do with tariffs. It doesn’t even appear in the section of the United States Code — Title 19 — that deals with trade. Rather, it is codified in Title 50, which covers “War and National Defense.”

Congress passed the law in 1977 to enable presidents to deal quickly with a national emergency during peacetime by ordering sanctions against, or freezing the assets of, a hostile foreign power or terrorist organization. The legislative text refers to an “emergency” that gives rise to “an unusual and extraordinary threat” — in fact, lawmakers specified that “emergencies are by their nature rare and brief, and are not to be equated with normal, ongoing problems.” That clearly excludes the supposed emergency identified by the Trump administration to justify its punitive “Liberation Day” tariffs, namely the trade deficits the United States runs with many trading partners. Those deficits have persisted for decades. They are not “unusual and extraordinary.” They are also, nearly all mainstream economists would agree, not a threat.

Even if America’s trade deficits did fit the IEEPA’s definition of “emergency,” that would not empower Trump to impose new tariffs or taxes on American citizens. (It is common to speak of levying tariffs against other countries, but tariffs are taxes paid by US businesses, which are typically passed along to US consumers through higher prices.) Nothing in the statute empowers presidents to mandate tariffs, which is why none of Trump’s predecessors ever tried to do so. To be sure, there are laws that delegate limited tariff authority to presidents. But that authority is constrained by detailed fact-finding requirements, is restricted to specified circumstances, and takes effect only after a lengthy public comment period.

Congress has never authorized presidents to impose tariffs at will. It couldn’t if it wanted to. Article I, Section 8 of the Constitution reserves to Congress alone the power to “lay and collect taxes, duties, imposts and excises,” and to “regulate commerce with foreign nations.”

All of which means that Trump’s new tariffs have no basis in law and amount to an assault on basic constitutional order.

These are not whimsical criticisms by liberal Democrats who oppose everything Trump does. They are the objections of prominent conservative and libertarian legal scholars like George Mason University’s Ilya Somin and of Trump-friendly advocates like economist Stephen Moore of Unleash Prosperity and US Senator Rand Paul, a Kentucky Republican.

In two lawsuits filed this month, one spearheaded by the New Civil Liberties Alliance, the other by the Liberty Justice Center, a half-dozen American companies are asking federal courts to strike the tariffs down as unlawful, based on the plain language of the IEEPA. They argue as well that to uphold the sweeping tariff authority claimed by the White House would violate the Supreme Court’s major questions doctrine. Under that rule of statutory construction, judges cannot assume that the executive branch has the authority to make “decisions of vast economic and political significance” unless Congress, using clear language, has granted that authority. It cannot be merely inferred.

Many legal challenges to the Trump administration’s radical policies are now in the pipeline, but these lawsuits go to a fundamental principle of the American system: the abhorrence of one-man rule. When the Minutemen at Concord and Lexington ignited the American Revolution 250 years ago, Senator Paul observed recently, they were motivated above all by the conviction “that no one should have taxes imposed on them without their consent.” So insistent were the Founders on keeping the taxation power out of the hands of a lone ruler that the Constitution requires all tax bills to originate in the House of Representatives. “Rule by one person,” Paul declared, “is contrary to everything our country was founded upon.”

As a matter of economics and international trade, Trump’s sweeping imposition of tariffs is wretched public policy. Worse than that, it amounts to a scandalous attack on the foundations of American law and liberty. What is at stake here is more than tariffs. It is a matter of who governs in a free society. If this power grab stands, the separation of powers will not.