The email, titled “meeting”, went to an unknown number of recipients, US officials in Canberra confirmed.
It was accompanied by a photo of a cat wearing a Cookie Monster outfit and holding a plate of biscuits.
In a light-hearted apology, the embassy called the email a “training error”.
“Sorry to disappoint those of you who were hoping to attend this ‘cat pyjama-jam’ party, but such an event falls well outside our area of expertise,” US mission to Australia spokesman Gavin Sundwall told the Australian Associated Press.
“It was a training error made by one of our new staff testing out our email newsletter platform.”
The US embassy in New Zealand, however, didn’t miss a chance to weigh in.
Along with the words “cat pyjama-jam”, the email also included words in Latin, and recipients were given an option to reply to the invitation.