Madison Decor has been a supplier to Engie for eight years enjoying a successful relationship with the main contractor.
But that suddenly turned sour on the site where Madison was working on a £600,000 interiors package.
Madison managing director Phil Williams claimed his firm was asked to leave the job after filing an official complaint about members of the Engie site management team.
Williams said: “Our work has been to the usual high standard and we have previously enjoyed a long and successful relationship with Engie.”
But Williams was unhappy about the conduct of some of the site bosses and filed a complaint to Engie.
He said: “Engie has a whistle blowing policy in place but now it looks like we are being punished as the whistleblower.
“We took delivery of £58,000 of flooring that morning then after helping unload it my employees were barred from the site.
“We have been paid the money for the work so far but we believe this is a breach of contract and will be making a claim.”
Engie declined to comment because it is now a legal matter.