The plant operators skills card scheme has been plagued with problems since late last year when the renewal system was transitioned over by new owner NOCN.
The Enquirer has learned about one training provider who has logged every call by staff to the CPCS lines since December.
The company has racked-up more than 26 hours of calls on the premium lines costing nearly £500.
The firm is now threatening to invoice NOCN for its phone bills.
The revelation comes as Unite demanded a showdown with NOCN and former scheme owner CITB.
Unite national officer for construction Jerry Swain said: “As it currently stands the CPCS card scheme is not fit for purpose.
“It is essential that problems to the CPCS card scheme are swiftly resolved. A backlog in renewing and issuing cards is denying skilled workers the ability to earn a living.
“If the problems are not swiftly resolved then the entire scheme will be undermined, which will result in major safety implications for the industry.
“While the problems with the scheme have arisen under the auspices of NOCN, the CITB which previously owned the scheme also have a moral duty to assist in resolving the problems.”
A CITB spokesman said: “CITB is very concerned about the problems within the operations of the CPCS cards scheme and is in close contact with NOCN to help them resolve this difficult situation as soon as possible – and we are told that the backlog is gradually reducing.
“NOCN purchased the scheme in February 2019, and we have worked with NOCN since then and will continue to support them for as long as it takes to return to a situation where people’s ability to work is not disrupted.”