Girls who wear "inappropriate" low-waisted or skin-tight trousers to a school in South Gloucestershire are to be asked to change on arrival.
Parents of children at Bradley Stoke Community School have been told tight trousers were "particularly unflattering" to some pupils.
From 8 November tailored trousers will be provided and girls asked to leave something of value as a deposit.
This will continue until they wear more appropriate trousers, the school said.
Parents were told of the ban in the school newsletter.
It said the "Miss Sexy or similar" trousers were inappropriate for school and their low cut meant that "undergarments and sometimes more are revealed".
The school said its uniform policy had been in place long enough for students to comply.
"I know from conversations and correspondence with some parents/carers that daughters are refusing to wear the right trousers rather than parents/carers refusing to buy them," the school newsletter added.
Bradley Stoke Community School has 750 students aged between 11 and 16.
In October 2009 Nailsea School in North Somerset disciplined 10 girls for wearing tight trousers after the head teacher banned them for "having visible zips and being too tight".