Campaigners in Tanzania have criticised some schools for making HIV-positive pupils wear a red ribbon on their uniforms.
The headmaster of one school told the BBC it was done at the parents' request to ensure that all sickly pupils do not do tasks that may affect their health.
But such stigmatisation was against the law, punishable by up to three years in jail, a campaign group warned.
The health minister has said he cannot comment until it is investigated.
According to UNAids, about 5% of the population - 1.4m people - in the East African nation are living with HIV.
The BBC's Aboubakar Famau in the main city of Dar es Salaam says activists have reacted with horror to the labelling of pupils in the Kibaha district.
They believe at least seven schools in the area, about 40km (25 miles) north-west of Dar es Salaam, are using the ribbon system.
"They are only doing that because they want to identify those who are HIV-positive," said Jane Tibihita, a co-ordinator of Upendo Partnership, a local campaign group.
Rebecca Mshumbusi, chairperson of the Kibaha Association of People Living with HIV/Aids, said it was unethical to reveal a person's health status in public.
"The information of one's sickness is confidential unless if one decides to share it with others. There are laws that can punish those revealing other's health status," she told the BBC.
But Mohammed Lukema, the headmaster of Kibaha Primary School, said he is only carrying out parents' wishes and pupils wearing a red ribbon were excused from any rigorous school duties, such as sweeping the compound and fetching water.
"Our school has pupils who are suffering from various diseases. The school and the society at large have decided to label pupils' uniforms," he said.
"In our school we put a red label on the pupils' collars to identify them."
The root of the problem is that there have been few initiatives to educate people about stigmatising those with HIV, Ms Tibihita said.
"They are only dealing with infection and prevention of the disease," she said.
"Now, the HIV and Aids Prevention and Control Act allows one with concrete evidence to be taken to court on the grounds of stigmatization and one can be sentenced for up to three years."