The BBC reported it was given dozens of messages shared within the chat by a member of the group.
Some of the posts referenced the government's Rwanda policy, while others joked about recent flooding in Pakistan, which left almost 1,700 people dead.
The six ex-officers, who were not serving at the time the messages were sent, will appear at Westminster Magistrates' Court on 7 September.
Tim Hayes, an employment partner at BDB Pitmans, said group chats between colleagues can blur the line between employees' work and social lives.
Speaking to HR magazine, he said: “The lines between the work and private communication spheres have become increasingly blurred in recent years and it is now relatively common for work colleagues to have their own WhatsApp groups for communicating about work issues.
“The fact that those apps are typically used for communicating in the private sphere has lulled workers into a false sense of security when it comes to what they can and can’t say about workplace issues.”
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However, Hayes said social media can be classed as evidence and need to be disclosed in legal proceedings.
He added: “In a recent case, a solicitor even lost a claim that her private messages were misused by her former employer when the employer disclosed them without her consent in the context of employment tribunal proceedings.”
Hayes said employees should be aware that they could face disciplinary action because of messages, even if they are not on work devices.
He said: “The risks are particularly high where the comments made on private devices or apps identify the employer and could lead to reputational damage, which might ultimately make the employer more inclined to take action.
“Given the risks inherent in social media communication, the best approach to adopt is simply not to write anything that you wouldn’t be happy being read out in court.”
