Dhakirah Salim, 19, wanted to take part in Miss England with her 22-year-old sister Latifah but was stopped because small print on the entry rules said mums and married women couldn't enter.
The disappointed young mum had gone along to support Latifah who was entering the contest but then decided she would also put herself forward.
But she was told because she has a daughter Sapphire, three, she couldn't take part part.
Dhakirah told her local paper: "This rule sends out the message that there's no beauty in women after birth and that young mums can't be good role models.
"I think that's discrimination towards women with babies."
The Miss England beauty pageant said the rule exists to protect young families because the busy schedule for contest winners is not compatible with having a settled home life.
But Dhakirah slammed the rule as unfair.
She said: "I'm attending college, I do extra-curricular courses and I do a part-time job that I travel around Birmingham and the UK for.
"I don't think it's fair that because I have a baby I shouldn't be able to enter the Miss Birmingham contest.
"I do get a lot of negativity about young mothers, and especially the perception of single mothers, but I hope to prove everyone wrong.
"They're trying to say women with children can only be housewives. Women should be able to go out there, seize opportunities and create a better life.
Angie Beasley, Director of Miss England, said the rule was in place to protect the 'family unit' because of the winner's demanding schedule.
She said: "I don't think it's old-fashioned. It's to protect families.
"We don't want to be responsible for splitting a mother up from her children."
She added: "There are other competitions that are less demanding, where ladies who have children should enter.
"I couldn't enter a baby contest because I'm not a baby. I don't fit into those rules. People have challenged this rule before but we are not changing it."
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