St Clare's Catholic Primary School in Birmingham has met with equality leaders at the city council to discuss a complaint from the pupil's family.
The council is supporting the school to ensure its policies are appropriate.
But Muslim Women's Network UK said the school was not at fault as young girls are not required to wear headscarves.
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The Handsworth school states on its website that "hats or scarves are not allowed to be worn in school" alongside examples including a woman in a headscarf.
Labour councillor Waseem Zaffar, cabinet member for transparency, openness and equality, met the school's head teacher last week.
In a comment posted on Facebook at the weekend, claiming the school had contravened the Equality Act, the councillor wrote: "I'm insisting this matter is addressed asap with a change of policy.
"Senior education officers from Birmingham City Council will also discuss this matter with the concerned school early next week whilst the head and governors discuss their next action."
In a council statement, Brigid Jones, cabinet member for children, families and schools, said: "Each school's governing body is responsible for the creation and implementation of its own uniform policy.
"However, the local authority is supporting the school to ensure its policy is appropriate, in line with legal requirements, and we are engaging with all schools to remind them of their responsibilities when it comes to setting school uniform policies."
Shaista Gohir, from Muslim Women's Network UK - which works to improve equality for Muslim women and girls, said: "The school is allowed to set its uniform policy and  schools do have to be mindful and inclusive and cohesive and make sure that they don't breach their duties under the Equality Act.
"But they haven't done anything wrong because there is no Islamic requirement for a four-year-old to be wearing a headscarf."
The school has not commented.
A school has been accused of breaching anti-discrimination laws after claims a four-year-old Muslim pupil was told she could not wear a headscarf.