What: Information-technology service company BT Group (NYSE:BT) plummeted as much as 19.4% on Friday following the United Kingdom of Great Britain's vote to exit the European Union, or a vote being referred to as "Brexit." Shares ended the trading day down 18.2%.

Image source: BT Group.

So what: While Britain banks were hit hard on Friday as global markets face uncertainty about what Brexit means for the British economy, many British-based tech companies with multinational operations were hit hard, too. Investors are concerned that information-technology companies like BT Group could lose their unrestricted access to the EU, and hence make competing with other EU companies difficult.

BT Group is a communications-services company with multinational reach, and many investors may be wondering if the company's information-technology services will be at a disadvantage, or even compromised.

Now what: The implications of the Brexit and how it will impact companies like BT Group are still unclear. Perhaps BT Group will provide a press release detailing how management plans to navigate through this uncertain time.