The Health and Safety Executive (HSENI) is trying to establish whether pupils in Northern Ireland have been affected by asbestos in science classrooms.
Its action comes after the HSE in England warned that some metal gauze mats used with Bunsen burners contained asbestos.
The risk of exposure is "low", according to the HSE.
It has told two UK companies to stop supplying the affected gauze mats to schools.
But the NASUWT teaching union has written to the Department of Education (DE) to make the names of the two suppliers public.
In a letter to the DE permanent secretary Derek Baker, the NASUWT's general secretary Chris Keates said the HSE's announcement would cause "deep concern."
As well as calling for the names of the two firms to be revealed, she called for more advice to be issued to schools.
"The NASUWT believes that it is essential the government investigates why it has taken so long for it to be identified that these suppliers are using hazardous materials," she wrote.
"Thousands of pupils and school staff could have been exposed to this."
In response a DE spokesperson said the department is "working with the Education Authority and the Health and Safety Executive NI to establish the position in Northern Ireland."
A spokesperson for Education Authority said: "The Education Authority is aware of ongoing investigations by Health & Safety Executive GB and Health & Safety Executive NI around metal gauze mats containing asbestos."
"We continue to work with HSENI in establishing any issues affecting Northern Ireland as part of the UK-wide review and we will keep schools updated."
In a statement, the HSENI said it is "aware of the ongoing investigations into the gauze mats and are in discussions with the Department for Education and the Education Authority."