Officials at the Unite union are now renewing their call for more direct employment in construction and an end to the widespread use of payroll firms.
Their use is so endemic that one leading labour and logistics firm even has its own sister payroll business to employ workers through.
The Enquirer has seen payslips from workers on major construction sites in London.
They are working as security guards, sweepers and traffic managers on jobs earning just above the London Living wage of £10.20 an hour.
Every week they then have £22.75 deducted as a fee for the payroll firms.
Unite London Region Officer Harry Cowap said: “These workers have no choice – they are forced to work through a payroll firm.
“It’s not like electricians or other skilled workers who may be able to claim something back in expenses.
“These workers – who are the lowest paid on site – are simply facing another fee for being employed through a payroll company designed to save money for the firms who should be really employing them.
“It’s a scam which has spread like a cancer through the industry and needs to be stopped.
“Workers also lose out on holiday and sick pay rights – even though they are working on some of the most prestigious jobs in the capital.”
Some major projects like HS2 are now vowing to prioritise direct employment.
An HS2 spokesperson said: “In April 2016, HS2 Ltd. signed an agreement with the TUC demonstrating our commitment to work together with the trade union movement to lead a safe, diverse and inclusive workforce with a strong voice.
“As well as establishing our support for direct employment in work packages, that agreement also underlines our responsibility as a direct employer as well as a commitment to the wider workforce that will deliver HS2 across our supply chain.”