Without mentioning their names, the US Department of Justice has put Facebook, Google, Amazon and Apple on notice.
"The department’s anti-trust division is reviewing whether and how market-leading online platforms have achieved market power and are engaging in practices that have reduced competition, stifled innovation or otherwise harmed consumers," the DoJ announced last night.
There have been multiple anti-trust probes into big tech in Europe – three of which have resulted in multibillion-euro fines for Google – but the Americans have previously been loath to launch similar competition investigations.
Part of this discrepancy is ideological: since the Reagan administration, US anti-trust regulation has focused specifically on whether anti-competitive markets lead to higher prices for consumers.
Such a limited focus makes it extremely difficult to take anti-trust action against Facebook and Google, even though they collectively make up 60% of the global digital ad market.
There is also a political resistance to taking on Silicon Valley: big tech is an American phenomenon and a massive creator of wealth, not only for the computing sector but also for health and retail. Tech is also a central battleground in the ongoing trade dispute beween the US and China. And let’s not forget how much big tech spends on lobbying US lawmakers.
But the mood could be changing. Senator Elizabeth Warren, a leading Democratic candidate for president, has proposed breaking up big tech, arguing that they have "too much power". Last month, there was a bipartisan bill in the Senate to force tech companies to disclose how much money they make from user data.
The timing of the DoJ's announcement also coincides with Facebook, Google owner Alphabet and Amazon reporting their quarterly financial results later this week.
This means investors should be asking more questions as the likes of Mark Zuckerberg and Sundar Pichai take part in their earnings calls in the coming days.