A NUT spokesman said no-one had complained about the incident
A teacher has been suspended by a school in Derby for making pupils do press-ups when late for registration.
The head teacher at Derby Moor Community Sports College said the teacher involved had used an "unacceptable sanction".
Wendy Whelan said parents were being kept informed.
But Ian Jennison from the National Union of Teachers (NUT) said no pupil or parent had complained, and the suspension was disproportionate.
He said: "It's an incident that I would not in any way consider to be gross misconduct.
"Gross misconduct would be where a member of staff has hit a child or embezzled money, something of that nature and that's the only thing you can be suspended for.
"In my view, a quiet word in the member's ear would have put an end to this, without it going all this way to the press."
Ms Whelan said an investigation had started and appropriate action was being taken.