A survey by the ACE trade body found that 20% of its smaller member companies had bills outstanding for more than 100 days.
Nelson Ogunshakin OBE, chief executive of ACE, said: “With increasing financial pressures facing client companies in the public and private sectors, small engineering companies are facing significant waits to be paid for the vital work that they do.
“This can cause significant risks for their business as cash flow proves tight and lending conditions remain difficult.
“We appreciate the government’s commitment on this issue through long-standing measures such as the Fair Payment Charter with maximum 28 days on payment.
“However, we hope to see the principles behind this adopted more widely across the sector , if we are maintain a sustainable industry.”
The survey quizzed firms with fewer than 50 staff.