Kate Hannah, 22, posted a furious rant on Facebook, accompanied by a picture of the grey, crew neck t-shirt that she says was deemed unacceptable by her boss.
She said that she wore the t-shirt to Bird and Beer in Beverley, East Yorkshire, after her manager's brother allegedly made an inappropriate remark to her.
There were even calls for her to take legal action after she shared her side of the story on social media.
She said on Facebook: 'So I've just got home after being sacked from my job, for refusing to wear a bra.
'Yesterday an inappropriate sexual remark was made to me, by my managers brother, and in the presence of her. I felt uncomfortable, objectified and shocked that this had happened.
'Unfortunately she saw fit to deal with the situation by telling me that I'm not allowed into work in future unless I'm wearing a bra. This was said to me in front of three other staff members and customers.
'Leaving me feeling body shamed and completely shocked that the blame was being put onto me that I had been sexually harassed at work. She called me stupid, silly and over the top when I told her I was upset.'
Most people appeared to agree she had been unfairly treated, with one person even suggesting an 'En masse bra-less protest' outside the American-themed venue.
Another added: 'I would seek legal advice, totally appalling'.
However, others sided with her employers, suggesting that abiding by uniform was a standard part of working.