NatWest Group has blocked messaging services WhatsApp, Facebook Messenger and Skype on company devices 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.
Banks in the US have been handed fines worth more than $2.8bn (£2.18bn) over the past few years over record-keeping rules – with workers unable to retrieve old messages from some messaging services.
JPMorgan Chase, Wells Fargo, Bank of America and Citigroup are among those to be issued with penalties.
It was reported in August that the UK banking regulator, the Financial Conduct Authority (FCA), is considering a probe into how bank workers use messaging services.
It follows a fine issued by energy regulator Ofgem to Morgan Stanley over calls made on private phones over WhatsApp – breaching rules on record-keeping.
Outside of banking, there have been issues with staff using apps in the public sector, with questions surrounding how ministers have used WhatsApp for government business in recent years.
The UK Covid inquiry revealed officials and ministers had deleted WhatsApp messages exchanged during the pandemic.
That included then-prime minister Boris Johnson, with then cabinet member Penny Mordaunt telling the inquiry that two years of messages with him had disappeared. Johnson told the inquiry he had lost around 5,000 messages.
