If Mark Zuckerberg wasn't already worried about facing up to UK politicians, he jolly well should be now.
Facebook UK's head of public policy, Rebecca Stimson, has just been sent a pretty sternly-worded ultimatum by Damian Collins MP and Chair of the Digital, Culture, Media and Sport Committee. Zuckerberg now has two choices: he can comply with the UK government's request, or he'll be served with a formal summons the next time he sets foot on UK soil.
Collins' letter isn't the first one he's sent to Facebook. Back in March, a letter was sent to Mark Zuckerberg requesting he show his face before a committee to answer some questions about Facebook's "catastrophic failure."
Zuckerberg didn't comply with the UK government's request. Instead he sent his CTO Mike Schroepfer to get a grilling from MPs in his stead. A move that hasn't gone down too well among British politicians.
"The Committee feels that the evidence lacked many of the important details that we need. We therefore re-state our invitation to Mark Zuckerberg," reads Collins' letter. "Mr Schroepfer failed to answer fully on nearly 40 separate points," Collins continued.
The letter makes reference to reports that Zuckerberg will be "giving evidence to the European Parliament" in May, and states that the UK government would like Zuck to come to London before 24 May.
If Zuck fails to show his face in May, he now risks being served with a formal summons meaning he'll need to face parliament whenever he next tries to enter the UK.
Carole Cadwalladr, the Guardian investigative reporter behind the explosive Cambridge Analytica report, described this letter as "pretty extraordinary."
"Either Mark Zuckerberg comes voluntarily. Or, he'll face a summons next time he enters British territory," says Cadwalladr.
Over to you, Zuck.