St John Bosco College at Engadine has placed a temporary ban on students shopping at a nearby supermarket.
Parents say that at a recent school assembly, students from the co-educational high school were told of the new rule, which was put in place after reports of inappropriate behaviour.
The Leader understands the issue relates to apparent theft of items.
St John Bosco College principal Damien Carlton did not delve into specifics, but did say the matter related to poor behaviour.
"St John Bosco College Engadine has recently received reports from members of the community of students behaving inappropriately at Coles Engadine store," he said.
"In the coming weeks, students will not be admitted to the store in uniform unless in the company of a parent or other adult. This decision was made in consultation with Coles and will be reviewed in the next fortnight.
"Our school has introduced this temporary measure to support the community and Coles and to send a strong message to both the school and local community that the college does not tolerate any form of anti-social behaviour."
A spokeswoman for Coles confirmed there was a matter discussed between the store manager and the school but says the supermarket does not ban anyone from its stores.