Photo: Chad Crowe

Big Tech has far too much power. Lawmakers from both parties agree, but for years Congress has been all talk and no action. Meanwhile, tech giants are threatening to use their control over digital platforms to gain unfair advantage in other markets where competing products depend on access to those platforms.

Over the past 20 years, the scope of commercial and personal activities relying on access to digital platforms has mushroomed. A few giant companies—Google, Apple, Amazon, Facebook—have achieved monopoly or near-monopoly control over key platforms, among them online search and advertising, mobile operating systems, online marketplaces, maps and social media.

All these dominant platforms, though distinctive, pose the same threefold danger. First, they have a chokehold over essential channels of communication and commerce, allowing them to be gatekeepers to the digital world. Second, they vacuum up a trove of personal information about users—what they see, hear, read, think and buy. This raises profound privacy concerns and permits these companies to manipulate users’ beliefs and behavior. Third, they distort the “marketplace of ideas.” The gatekeepers can shape the flow of information to advance their own economic and political agendas.

Case-by-case antitrust litigation alone won’t rein in Big Tech. Unlike regulatory power, which entails actively supervising an overall market and setting uniform rules for it, antitrust litigation is slow. It can target only discrete transactions or instances of wrongdoing by individual companies. That approach can’t produce a coherent response to the multifaceted problems caused by Big Tech’s dominance.

A lot of energy has been misspent arguing whether Big Tech dominance arises from misconduct. That is beside the point. When serious anticompetitive conditions arise in markets providing critical services to the public, regulatory intervention may be needed whether or not those conditions involve misconduct. The U.S. often has regulated markets involving competing networks, such as transportation, media, broadcast, cable and telephone. As in Big Tech, the largest player’s power tends, absent intervention, to snowball quickly into a monopoly.

I argue in my recent book that Congress should adopt a limited regulatory framework opening the markets dominated by Big Tech to more competition. But as Congress has dawdled, another pressing danger has emerged. The tech giants are moving into new markets in which products and services depend on access to their digital platforms. Since their competitors’ products must have access to those platforms—for example, smart home devices need access to Apple and Android mobile platforms—the tech giants can seize an unfair advantage by giving their own products access of better quality or on better terms.

As more products and services depend on digital platforms, the number of markets vulnerable to these tactics rises. Big Tech has made inroads into “smart” homes, automobiles, payment systems and healthcare. The mind boggles at the prospect of the digital aspects of these markets, including mountains of private customer information, being absorbed into the Apple or Google ecosystem.

Congress must act quickly to prohibit the tech giants from unfairly leveraging their dominance into more markets. This doesn’t mean rewriting the antitrust laws but rather taking these three steps:

First, prohibit dominant platforms from giving their own products an unfair advantage by reserving for themselves higher-quality access than they grant competitors. Amazon was charged by the European Union for excluding rival merchants’ products from the “Buy Box”—a valuable space on its website that helps generate sales. Amazon settled the case, agreeing to give competitors’ products the same placement as its own. EU regulators were right and Congress should prohibit a dominant platform from giving preferential platform access to its own products.

This same rule should apply when the platform provides a function through hardware rather than software. Apple has installed a “near field communication” chip in its phones to complete secure short-distance mobile payments with its Apple Pay service, but it excludes other mobile wallet payment services from access to the chip. This discriminatory access relegates competing payment services to lower-quality connectivity. The EU has said it has an eye on the matter.

Second, prohibit Big Tech from using dominant platforms to extract competitors’ business data and exploiting that data in developing competing products. Last month, Amazon settled EU charges that it gleaned nonpublic information from independent merchants using its platform to inform Amazon’s own competing product offerings.

Apple and Google are entering the car-manufacturing business, and that market illustrates why Big Tech’s ability to extract data from competitors should be limited. Drivers should be able to use their cellphones easily in and outside their cars. Car makers can facilitate this by supporting interoperability between the phone and the car. But Apple and Google shouldn’t be allowed to abuse this capacity to gain access to user and vehicle data.

Third, protect consumer privacy. Congress has yet to address the massive amount of personal information these companies already collect. But the scope and scale of these data are about to explode as Big Tech hoovers up information from our homes, cars, financial transactions, healthcare and other markets. This will be augmented, before long, by a 24/7 flow of video, audio and electronic signals collected by their fleets of autonomous vehicles zipping about our streets. Add to this the capacity to sift data with artificial-intelligence tools, and things start resembling the dystopian surveillance societies portrayed in sci-fi movies.

It is past time for Congress to add real bite to its bark and address the harmful effects of Big Tech’s power. This should be at the top of lawmakers’ priorities for 2023.

Mr. Barr is author of the memoir “One Damn Thing After Another.” He served as U.S. attorney general, 1991-93 and 2019-20.