Helen Simpson, 33, from Nottingham, was wearing a low-cut, black evening dress when a woman staff member told her to cover up or leave.
"She said I was wearing too low a top, which people found offensive," Simpson said. "I was highly embarrassed humiliated, absolutely humiliated.
"There were girls at the casino wearing short skirts that I think are nothing more than belts.
"I feel like I've been discriminated against for having big breasts."
One of Simpson's group lent her a zip-up top to cover her chest, but the night got worse when she learnt bar staff, croupiers and security staff had been told.
Simpson, a business manager for McDonald's who is in her third year studying human resource management, said the matter had been handled unprofessionally.
"The most humiliating thing was that everybody knew," she said.
"All the staff were staring and the group of guys that complained I'm sure it was them were smiling."
Simpson has written to casino management saying she left feeling "humiliated, discriminated and highly embarrassed".
She wrote: "Being well-endowed in the upper region is something I did not choose in life and something I'm certainly not proud of.
"In turn, have you ever been shopping for a formal cocktail dress that is accommodating to a size 14 woman with the top half demanding a size 20?"
Simpson said it was discrimination. "You don't see women with too small boobs being criticised, do you?"
Her boyfriend, Chris Olivier, 34, said he had found Kiwis polite, friendly people, and the treatment had surprised him.
"She'd changed quite a few times before we went out and I thought she looked really nice," he said. "It's just disappointing."
Casino chief executive Brett Anderson said he questioned Simpson's motives in contacting the media and he would respond to her personally.
"The person on duty at the time made a judgment call based on feedback," he said.
"Perhaps it could have been handled a little bit better, but these are things I'll discuss when I draft a letter. It's not so much a matter of dress code than comments were received from people. I'm not going to discuss this through the media."
- The Press
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