The Swedish Schools Inspectorate said an official complaint against the International English School in Uppsala -- submitted by a relative of a pupil -- led to an investigation into the policy at the school for children ages 9 to 12, The Local.se reported Thursday.
The complaint argued the "disciplinary contract" goes too far by saying students would be disciplined for calling teachers by their first names, a common practice in Sweden, and girls would be punished if their bra straps show through their clothes.
School Principal Mikael Ostling said before the ruling students rarely face punishment for most of the offenses because the pupils respect and follow the rules.
"We think a distraction-free learning environment is more important than being able to show your underwear," Ostling said in April. "We follow the Swedish school laws, but we also have an Anglo-American heritage, which we are proud of and enhances our profile."
The directorate said the disciplinary contract the school requires students and parents to sign at the start of the term is unlawful. The contract outlined the offenses that could lead to detentions.