Ms Amy Cheong, 37, a University of Western Australia graduate, had worked full-time for slightly more than a year at NTUC headquarters before her services were terminated on Monday.
As assistant director in NTUC's partnership alliance section, Ms Cheong planned membership programmes, but was not involved in union work.
She is believed to have once worked in sales at the Marina Mandarin Hotel.
The Straits Times was unable to reach her on her mobile phone, or to verify her marital status through her former employer, NTUC.
Three co-workers contacted by The Straits Times said she was an outspoken, brash person.
From her Twitter account, it was clear she had spent the early hours of Monday morning doing damage control, with 78 tweets apologising to individuals who had contacted her.
One read: "Thank you to all who accept my apology. I have learnt a huge lesson from this. I am really sorry."
But Ms Cheong also appeared to have briefly lost her cool in response to a tweet publicising her offending posts.
She vented: "It's people like you that make this an issue about racism when it's not. It's a stupid comment, but not meant to be a racist one."
Soon after, her account went silent, at around 5am.