NatWest Group has blocked messaging services WhatsApp, Facebook Messenger and Skype on company devices in the UK to stop staff using them to communicate with each other.
The bank had already told employees to stick to “approved channels” for conversations about business matters.
But now it has gone further and made the platforms inaccessible on work phones and computers.
So-called off-channel communications are a persistent problem in both business and politics, with concerns that services such as WhatsApp are used to reduce the scrutiny some conversations can be subject to.
Messages can be difficult to retrieve or even set to disappear – whereas those sent via approved channels are fully retrievable, meaning they can be looked into if there is any suspected wrongdoing.
“Like many organisations, we only permit the use of approved channels for communicating about business matters, whether internally or externally,” NatWest said in a statement.
It said the change came into effect earlier this month.