The sudden outbreak of orders from bogus and cloned firms has caused the industry trade body to raise the alarm about the swindle.
More than £112,000 of mesh has been reported to have gone missing in the last week alone.
But the British Association of Reinforcement believes the full extent of the scam has not fully come to light and could run into millions of pounds.
Steve Elliott, BAR chairman, said: “These are sophisticated scams and reinforcement suppliers are strongly advised to carry out stringent checks right down to the telephone number.
“Be cautious if the delivery address is an isolated warehouse with no construction going on or if the priced agreed is higher than the real worth.”
The use of clone companies to defraud manufacturers and suppliers has been seen in isolated cases for years, particularly in the plant and equipment side.
But now the fraudsters are switching to the rebar industry as the price of mesh hits £450 a tonne.
The latest attacks also suggest that fraudsters are now more sophisticated and systematic.
One supplier said he believed his supplies had been sold on as imported Italian mesh with forged certificates.
BAR has warned suppliers to tighten up on vetting and due diligence procedures. Credit insurers have said they will not cover any loss if they believe that sufficient background checks have not been made.
Some bogus companies have slipped through supplier checks in the latest spate of attacks.
Around 250 tonnes of mesh is known to have been stolen with one fabricator hit for 100 tonnes.
But the problem is feared to be a lot bigger as scammers move to use ‘clone’ genuine companies to place orders.
Here a reputable company is cloned. All will be correct apart from the telephone numbers and email addresses.
The clone company takes delivery of reinforcement mesh and then sells the mesh on.
Elliott said: “This make it essential that the reinforcement sector continues to share information to beat the scammers.”