In a 5-4 ruling along party lines on Monday, the court, featuring Justice Neil Gorsuch rather than Judge Merrick Garland, ruled that American Express did not violate antitrust laws when it wrote into its contracts with retailers that they could not offer discounts or enticements to get customers to use other forms of payment.

But it could prove to be one of the most consequential rulings of the decade, serving as a broad immunity cloak for Silicon Valley giants — and perhaps others — in their quest to utterly dominate the global political economy.

But the way in which Justice Clarence Thomas decided the case could make it applicable to any company that serves as a conduit between consumers and businesses, in what is known as a “two-sided market.” That would include Google and Facebook, which match advertisers to web users; or Uber and Lyft, which match drivers to customers needing rides; or Amazon and eBay, which match sellers and buyers within its marketplaces.

Under the newly created American Express standard, a claim that Uber prevented drivers on its platform from working for Lyft, or that Amazon used its voice assistant to steer consumers to its house brands, would also have to harm consumers for it to be considered an antitrust violation. It’s not enough that suppliers or workers are screwed; for a violation to occur, the company must screw everyone at once.

This is obviously an invitation for many more creative forms of abuse. As long as prices stay low — in the case of Google and Facebook, they’re already at zero — platform businesses in multi-sided markets could, under the Supreme Court’s logic in American Express, do virtually anything to concentrate their power.

The ruling doesn’t make much sense as it applies to credit card firms either.

At issue are swipe fees, the hidden scourge of every retailer. Whenever you pay for something with a credit or debit card, the retailer has to send a fixed amount of that sale to the credit card company (and there are really only four: Visa, Mastercard, Discover, and American Express) to complete the transaction. These fees have spurred epic battles between two large industries — the credit card networks and the retail sector. This case involved one way retailers tried to get an edge: by steering customers away from the forms of payment that triggered the highest swipe fees, or in other words, by making the cards compete against each other in a market of sorts.

American Express, which caters to a higher clientele and offers generous rewards programs, is the clear leader in swipe fee charges, funding their generosity by extracting larger chunks from retailers. Some merchants simply don’t take American Express, but about 6.4 million locations do, ostensibly to attract wealthier customers. The transactions represent a wealth transfer, from poorer Americans who use prepaid cards or cash to high net worth wielders of platinum and sapphire rewards cards. Companies like American Express kick back some of the swipe fee revenue to their customers in rewards; they essentially pay less for the same products. That keeps high-income cardholders paying with American Express, generating more swipe fees.

To prevent steering from merchants, American Express forbids them from encouraging customers to use other credit cards, like by offering a discount or free delivery for using Visa. This, said the Justice Department and 17 states, including Ohio, wasn’t an example of competition — it was anti-competitive.

The gag order on information from retailers to customers keeps swipe fee costs inflated across the market, as trying to compete with lower fees would be futile. Indeed, from 2005 to 2010, American Express raised its swipe fees 20 times, secure in the knowledge that no retailer of significance had the ability to retaliate against them. And while cardholders did earn rewards, the vast majority of the swipe fees were kept by American Express.

But Thomas, writing for the court, ignored this evidence of anti-competitive conduct and determined that credit card markets were special because they catered to both retailers and cardholders. “Credit-card networks are best understood as supplying only one product — the transaction — that is jointly consumed by a cardholder and a merchant,” Thomas wrote. “Accordingly, the two-sided market for credit-card transactions should be analyzed as a whole.”

Therefore, because consumers benefit from using American Express — namely, splitting the profits with the company from high swipe fees — the company could not be said to have committed an antitrust violation, according to the Supreme Court. The ruling relied heavily on papers from economists who were paid by the credit card industry.

Thomas’s “two-sided market” claim is an invented rule, conjured specifically to aid American Express in its quest to extract maximum revenues from retailers. “I am not aware of any support for that view in antitrust law,” wrote Justice Stephen Breyer in a scathing dissent he read partially from the bench.

Whether or not consumers benefit from this situation — and most lose out — is immaterial to whether merchants are getting squeezed and would-be competitors are barred from gaining a foothold in the market. And indeed, Thomas neglected clear evidence that Discover tried, and failed, to compete by offering lower swipe fees, because American Express made such competitive efforts impossible through its contracts.

Despite swipe fees, retailers in America have managed to thrive for centuries, and they’ll surely pass enough costs onto their customers to survive after this ruling. The real trouble lies with other businesses that could try to use the “two-sided market” theory from this case to deflect their own antitrust violations.

Thomas wrote in his opinion that “it is not always necessary to consider both sides of a two-sided platform,” giving the example of a newspaper, which solicits advertising and subscribers. But you can think of many possible applications of Thomas’s brand new rule, particularly involving the tech industry. Indeed, the Computer and Communications Industry Association, a trade group for tech firms, supplied an amicus brief in favor of American Express.

As Breyer wrote, the majority decision could easily be applied to internet-based platforms that serve multiple markets, shielding those companies from antitrust law. It’s not like Google, Facebook, or Amazon need more help in their rise to power.

Allowing a restriction of competition in one side of a market as long as those on the other side are treated decently creates incentives for abuse of power. And Thomas defined “two-sided market” so broadly that practically any market that brings together buyers and sellers could try to qualify.

In a March op-ed, Lina Khan of the Open Markets Institute explained that if the Supreme Court ruled for American Express, “[tech] platforms will be able to engage in anticompetitive activity with one set of users, so long as they can plausibly claim that harmful conduct enabled them to benefit another group.” The risk is that tech platforms will simply be immunized, at a time when policymakers have begun to worry about their size and influence.

Removing the ruling from the field of antitrust may help expose the absurdity that underlies it. Excusing one crime because others may benefit would never be applied to, say, a burglar who sold the goods he stole at a steep discount to the public. Burglary is a crime, period. A factory (which brings together producers of raw materials and buyers of finished products) may be able to produce cheaper goods by dumping its toxic waste in the town reservoir or breaking minimum wage laws, but its owners would not plausibly argue that only two wrongs make a wrong. But when it comes to laws against anti-competitive behavior, the Supreme Court’s rationale is now different.

Tech firms wouldn’t be completely out of the woods; for example, the Federal Trade Commission is currently investigating Facebook for violating a 2011 consent order on data privacy, which doesn’t hinge on antitrust law at all. But this ruling will surely make it harder to use one robust set of tools to deal with the widening power of Silicon Valley. All because a financial company wanted to protect its outsized profits.