According to the Unite trade union, its members working for Mears in Tower Hamlets were told at a tool box talk that beards were now banned so that workers can “wear appropriate dust masks effectively”.

Unite has subsequently obtained a letter from the company confirming that: “This is now a Mears nationwide policy for the entire company.”

The letter adds that a goatee “may be acceptable so long as it does not hinder the correct fitting of said dust masks”.

Mears has said workers need to be clean-shaven in order to be safely fitted with a tight-fitting face mask when working in dusty environments, and exceptions are only made if a worker can’t shave or a mask cannot be worn for medical or religious reasons. But for the company to allow this either a medical certificate or a letter from a place of worship must be presented.

The decision was immediately criticised by Unite as “penny-pinching stupidity”.

Unite regional official for London Mark Soave said: “The arrogance of Mears is hair-raising. This is a highly delicate issue, which has huge cultural, religious and personal issues and where sensitivity should be the watchword. Instead members have been handed a decree from on high.

“This is clearly a case of Mears going for the cheapest option and amounts to ‘penny pinching stupidity’. Other forms of masks are available and these should be offered to existing workers.

“Unite will always put the safety of our members first and creating huge resentment and anger among your workforce is never the way forward. Mears needs to withdraw this decree and enter into a proper consultation with Unite and the workforce.”

Unite national health and safety adviser Susan Murray said: “An employer should first assess the risks presented by exposure to hazardous substances, then identify the steps needed to adequately control the risks; put them into operation and ensure they remain effective. The use of Respiratory Protective Equipment (RPE) may be one of the control measures, but the wearing of face masks should be a last resort and priority should always be given to eliminating the risk.

“Before any policy is introduced there should be full and proper consultation. It is crucial that the policy recognises the diversity of the workforce and the principle that workers should be consulted and given a choice of several correctly specified types of RPE so they can choose the one they like.”

But Mears has stood by its position, and the company’s group health and safety director, Mark Elkington accused Unite of not taking the safety of its members seriously “in order to make a cheap point”.

“We are pretty surprised that Unite, who claim to have the safety of workers at heart have taken this disappointing stance,” he said in a statement. “Every employer in the UK has a legal responsibility to ensure that employees working in dusty or otherwise potentially hazardous environments are properly protected and in recent years employers have been prosecuted for failing to fulfil this duty.

“The simple fact is that no dust mask can work effectively unless it forms a seal against the skin. That is not possible with a beard or even heavy stubble. If the Health and Safety Executive did a spot site visit and found workers wearing dust masks that were not sealed against the face then we would be liable to prosecution.”