Teachers in the North East are calling for a Maximum Working Temperature to be introduced.
As it stands, lessons have to carry on no matter how hot it gets inside.
A teacher from the North East is calling for more funding to better ventilate schools.
Nick Jones, a secondary school teacher in County Durham, along with other members of the NEU, say they want a maximum working temperature introduced, especially as they don't have the systems in place to control the heat inside.
"We are seeing students really, really struggling. Even with the best of intentions, it's very difficult to complete any task in this sort of heat."
"If this is something that is going to be happening regularly, which we can assume it is, it's going to come back every single year. It's coming back during exam periods... Having to sit through exams in these temperatures would be incredibly difficult."
Although it is generally accepted that people work best at a temperature between 16°C and 24°C, as it stands there are no specific legal maximum working temperatures for schools or for offices or other workplaces. However, there are some sources of legal protection for school staff and pupils, including The Health and Safety at Work etc Act 1974, which requires employers to ensure the health, safety and welfare of their staff and other present in the workplace (such as pupils).
"As it gets higher, you run the risk of sickness, dizziness, dehydration, students fainting... students with epilepsy are also badly affected."
Better ventilation is something that the NEU also called for before, as the pandemic started to hit in order to stop the spread of Coronavirus.
"That would have been particularly useful over COVID, system to circulate the air and to control the temperature would have been a huge benefit. It's a blind spot perhaps, that we've not had to deal with before, but it's certainly becoming a problem now."
Some MPs are also urging for a legal limit of 30°C in most workplaces or 27°C for those doing strenuous work guaranteed. It's to help protect employees from tiredness, infections, heatstroke and even death.
That means employers would have a legal duty to introduce "effective control measures", such as installing ventilation or moving staff away from windows and sources of heat, under the proposals.
A total of 37 MPs have signed a motion, tabled in the House of Commons by Labour's Ian Mearns (Gateshead), in support of the plan.
It comes as the Met Office warns parts of England and Wales could face extreme heat at the beginning of next week, with temperatures predicted to soar into the 30s.
The early day motion (EDM) states: "That this House notes that recent surveys of workplace health and safety representatives show that high temperatures are one of their top concerns.
"(It) regrets that workers in the UK have no guaranteed legal safeguards from working in uncomfortable high temperatures, and that the consequences of this range from dizziness, tiredness, asthma, throat infections and, in extreme cases, heat stroke and death.
"(It) insists that without recognised law, current recommendations for employers to maintain a reasonable temperature within the workplace are impossible to enforce unless a worker is seriously insured or killed from heat stress.
"And (it) calls on the Government to introduce legislative proposals to ensure a maximum working temperature of 30 degrees Celsius, or 27 degrees Celsius for those doing strenuous work, beyond which employers would have a statutory duty to introduce effective control measures, such as installing ventilation or moving staff away from windows and sources of heat."
EDMs allow MPs to express an opinion, publicise a cause or support a position. It is rare for EDMs to be debated.