Updated 1.20pm
The UĦM Voice of the Workers has ordered its bus driver members to refuse to drive buses when the temperature aboard soared over 30 degrees Celsius.
Temperatures higher than 39 degrees have been recorded on buses that have had to switch off their air-conditioning system to help curb the COVID-19 spread, the union is claiming.
It said it has been flagging the "unbearable heat" aboard buses for the past three weeks.
Air conditioning systems aboard buses have been switched off to reduce the risk of COVID-19 virus spread.
But the union said that bus drivers' health and safety was at risk due to the measure. The permanent opening of hatches in buses to allow for ventilation had barely impacted the high temperatures on buses, the union said.
Malta Public Transport, which operates the country's bus service, reacted in a statement.
The company said that it was abiding by public health authorities' instructions and noted that drivers had a window which they could leave open while driving.
"While the company acknowledges that on some days there are buses that, like all other vehicles, may reach a warm temperature while parked in the depots or terminals, it is also pertinent to note that the temperature is generally reduced once the bus is moving and air flows through the vehicle," MPT said.
Over the past weeks several precautions have been taken when it comes to public transport, considering that route buses are the only means of commuting for some people.
In March the Malta Public Transport had said buses were being fumigated during the night.
Then in May Superintendent of Public Health Charmaine Gauci said passengers have to wear masks on buses.