Last week, as Ukraine’s counteroffensive against Russia was gaining pace, former Russian president Dmitry Medvedev said that Russia could destroy the undersea cables connecting Europe and the US to the internet in retaliation for the West’s alleged involvement in blowing up the Nord Stream gas pipelines last year.

While it remains unclear who was responsible for pipeline attack, recent media reporting has suggested that the US was made aware in advance of the operation—which was allegedly carried out by Ukrainian forces—and passed that intelligence on to Germany and other European countries. In response, Medvedev, now deputy chair of Russia’s security council and a close ally of President Vladimir Putin, declared in posts on Telegram and Twitter that Russia no longer faced any barriers, even on a moral level, to destroying undersea cables.

While that might not seem as big a deal as Putin’s repeated allusions to using nuclear weapons, it’s a threat that shouldn’t be dismissed.

Undersea cables, also known as submarine cables, are the physical infrastructure that connects the digital world. Hundreds of fibre-optic cables, some no thicker than garden hoses, are laid out across the ocean floor, enabling the real-time global transmission of data and communications signals. These cables facilitate around 99% of internet traffic as well as the telephone calls, data transfers and other telecommunications that enable modern life to function. The first undersea telegraph cable was laid in 1858; today, there are almost 400, most of which are commercially owned and operated.

While Medvedev’s threat may have just been sabre-rattling, if Russia followed through on it and cut undersea cables, the consequences would be immediate and widespread.

An attack could suspend access to phone calls, messages, videos and streaming services. Health and emergency services would lose contact with each other and with the public, in many cases making them unable respond to calls for assistance, let alone coordinate to respond to or monitor major crises.

Payment systems and ATMs would be down. Trillions of dollars would be wiped off the European and US economies as banks were unplugged from the global financial system, with economic effects felt across the world. Workplaces and businesses that rely on the internet would also go down. Educational institutions would struggle to conduct online learning, impeding students’ education and limiting access to knowledge and resources.

E-commerce would take a hit too, exacerbating disruptions to supply chains and shortages of essential goods. Brick-and-mortar stores would be cut off from communication with suppliers, limiting access to food and other essential supplies.

Broader critical national infrastructure, from power grids to transportation networks and water networks, would be down too, since they rely on the real-time transmission of data through undersea cables.

Fixing the damaged cables would take some time, testing the social order of countries as public frustration mounted while essential services continued to be unmet.

NATO is taking this threat seriously.

Shortly after Medvedev’s comments, NATO announced the establishment of a new centre in the UK to monitor and protect against the threat of Russian sabotage to critical internet infrastructure. Russian ships have been actively mapping undersea cabling around Europe and investing in subsurface naval capabilities to target them for some time. The good news, however, is that Russia likely lacks the capability to carry out undersea cable attacks at a catastrophic scale. Undersea cables are spread out across the globe in international waters, meaning it would be difficult to completely cut off Europe’s and the US’s access to the internet.

Yet with the modern world so reliant on the digital connectivity that undersea cables facilitate, the reality is that even a targeted or crude Russian attack on a number of critical cables or a regional choke point could cause significant disruptions across Europe and the US.

Any Russian attempt to damage undersea internet cables would constitute a hugely disproportionate response to any alleged Western involvement in the Nord Stream explosions.

Such a move would not only undermine regional stability, but also propel the world perilously closer to the brink of an all-encompassing conflict.