Ofsted chief inspector Amanda Spielman risks splitting communities by backing head teachers who may wish to ban the hijab, says a teaching union leader.
National Education Union leader Kevin Courtney said she overstepped her remit in February when she backed an east London head who tried to stop pupils wearing the Muslim head-scarf.
He said heads should not ban the hijab without consulting the local community.
Ofsted said head teachers needed to be able to take uniform decisions.
But Mr Courtney said ahead of his union's conference in Brighton, he feared schools might introduce bans because they were frightened of Ofsted, which could then put social cohesion at risk.
Mr Courtney was referring to a speech in February in which Ms Spielman said: "School leaders must have the right to set school uniform policies in a way that they see fit, in order to promote cohesion.
"It is a matter of deep regret that this outstanding school has been subject to a campaign of abuse by some elements within the community.
"I want to be absolutely clear - Ofsted will always back heads who take tough decisions in the interests of their pupils."
She gave her backing to head teacher Neena Lall, of St Stephen's state primary, who had been involved in a row with Muslim community leaders over young pupils wearing the scarf in school.
Ms Spielman also said her inspectors would speak to pupils wearing the scarf to find out why they were doing so in school, adding that wearing it could be interpreted as ''sexualisation of young girls.''
A motion to be heard at the conference says that Ms Spielman went beyond ''the remit of Ofsted'' and that members should robustly challenge it.
An Ofsted spokesman said: ''The NEU's comments are disappointing. There's nothing political about ensuring that schools and parents aren't being subject to undue pressure by national or community campaign groups.
''Head teacher need to be able to take uniform decisions on the basis of safeguarding or community cohesion concerns and Ofsted will always support them in doing that.''
