Hundreds of schools have been ordered to conduct blanket criminal records checks on all staff in the wake of the sex offenders row.
Several local authorities have formally instructed schools to launch Criminal Records Bureau checks on thousands of staff, despite advice against such action from Ministers, the NASUWT teachers' union said.
Chris Keates, NASUWT general secretary, condemned the crackdown as a "gross over-reaction" and a waste of money.
The action followed the controversy over sex offenders being cleared to work in schools which engulfed Education Secretary Ruth Kelly last month.
Ms Keates said the action was a "gross over-reaction which would undermine the steps taken to restore parents' confidence in schools".
"The Department for Education and Skills has issued two letters to local authorities making it absolutely explicit that such checks are unnecessary."
Derby City Council is one of several authorities to have ordered the checks covering all staff, including teachers, cleaners and dinner ladies.
Carol Mee, spokeswoman for Derby City Council, said about 100 schools in the area had been instructed to conduct the checks as soon as possible.