Lauren Parkes from Willenhall was at The Hangar in Pearson Street, Wolverhampton, on February 24. She said she encountered a security guard when she went to queue for the disabled toilet.
She said the guard tried to turn her away as he did not believe she was disabled, resulting in her showing him her stoma bag.
Lauren said: "I am appalled. I'm so shocked. I was with my friend who has colitis and had an 'I can't wait card' as she has an invisible disability.
"We had to prove something was wrong with us. I have Crohn's, that should be enough to be able to use the disabled toilet.
"I did get my bag out, but luckily for me I am quite a confident girl and my stoma bag has made me more confident.
"On the night, I was speechless. I really wasn't expecting for my disability to be questioned. It's discrimination. They're gatekeeping who is and isn't disabled."
The 25-year-old, who works in social media management, added: "I have a right to be using that toilet. Not every disability is visible, but he was turning everyone away because we didn't look disabled."
When contacted for a statement, the security team at The Hangar initially claimed that staff had apologised to Lauren, met her on the way out of the club to shake her hand, and offered her a free ticket for another day.
However, Lauren disputes this, and said: "That's what I'm really annoyed about. Nobody has spoken to me.
"No one met me at the door, nobody shook my hand, and I haven't been offered a free ticket as a gesture of goodwill."
A spokesman for The Hangar said: "The Hangar treats the safety of our guests as a top priority. And to reflect this we support and work alongside West Midlands Police to maintain the four licensing objectives, and our license conditions.
"This complaint will be investigated with relevant departments and with TLG Security who provide the security at The Hangar.
"Although the conditions require us to be stringent, we are also very understanding of any personal circumstances that could leave a guest feeling uncomfortable at the entry point.
"Please be assured as with any, this complaint will be handled with the utmost care and consideration and any results be fed into our training procedures."