Dundee City Council signed a “construction charter” with Unite last December pledging direct employment on public jobs.
But local Unite officials discovered workers on the Hill Street housing site were being employed through an “umbrella” company.
A spokesperson for Robertson Partnership Homes said: “Robertson is committed to working in partnership with Dundee City Council and has done so for many years.
“Robertson Partnership Homes commenced on site at Hill Street in Dundee in April 2018 – around eight months prior to the Charter being signed by Dundee City Council and Unite.
“Since being made aware that Unite expected retrospective compliance, the three temporary agency workers on the Hill Street site have been moved to PAYE by the agency.
“Robertson remains a responsible employer and is committed to an ongoing relationship with Dundee City Council.”
Unite said: “Agencies attempt to force workers in to so-called ‘umbrella companies’, to off-load national insurance contributions and other benefits to the detriment of the worker.”