Governors at schools placed in special measures for failing to protect children from the risks of extremist views are to be interviewed as part of the council's investigation.
They have been asked to sign a form which warns them that any information they give may be shared with the police and the Peter Clarke inquiry - the counter terrorism expert hired by Michael Gove who is also investigating the allegations in a separate investigation.
Ofsted launched an investigation into 21 schools over allegations of involvement in a takeover plot by hardline Muslims, of which five were placed in special measures after being rated "inadequate" earlier this month.
Birmingham City Council - which has been conducting its own independent review into the claims, headed by Ian Kershaw - has now begun interviewing governors from these schools.
It remains unclear whether all governors from all five schools are being questioned.
A leaked letter shown to ITV News by one governor states that evidence or personal information gleaned from those inquiries may also be passed on to education commissioner Peter Clarke's probe into the "Trojan Horse" allegations and used as evidence in any criminal investigation.
The governor said:
Why are they asking governors to sign this?
People are scared and feel they can't talk freely or openly and are worried what they say maybe taken out of context or misrepresented.
The former anti-terror chief's report is expected to be published in July.