A receptionist was sent home from work for refusing to wear high heels.
Nicola Thorp, 27, from east London, was told she needed arrive at accountancy firm PwC wearing two to four inch heels.
The 27-year-old from Hackney complained the policy was discriminatory because men could wear flat shoes.
Ms Thorpe was being employed by PwC's outsourced reception firm Portico.
She told ITV London: "I turned up for work wearing smart flat shoes and was told you can't wear those, you need to go and wear heels.
"I said I don't have any with me and I don't think it's right that you are expecting me to work a nine-hour shift on my feet escorting clients around the building.
"They said fine, you can go and buy a pair and I'll let you work or you're going to be sent home.
"I pointed to a male colleague and said he's wearing smart flat shoes, I'm wearing smart flat shoes, what's the difference here?
"And I was laughed at because I was making it a sexist issue, which is what I believe it is."
Employers are allowed to dismiss staff who fail to meet reasonable dress code guidelines, if they have been given time to buy the right clothes.
She is also pushing for employer's dress codes to be debated in parliament.
Simon Pratt, Managing Director at Portico who employed Ms Thorp, said in a statement:
A PwC statement said: "PwC outsources its front of house/reception services to a third party supplier.
We first became aware of this matter on 10 May some five months after the issue arose. The dress code referenced in the article is not a PwC policy."