This came to light after Commissioner Kevin Dunion ordered Scottish Water to provide UNISON with full financial information on its PFI wastewater contracts, over-ruling their objections that this would substantially prejudice the confidentiality of commercial or industrial information.
The nine contracts, most of which run for 30 years, cost nearly £600 million in capital costs and around £130 million annually.
UNISON Scottish Organiser Dave Watson said: “For too long commercial confidentiality has been used to keep the true costs of PFI from the public. This decision shows how important it is for Freedom of Information legislation to be extended to cover private companies providing public services as so many are not covered, including the privatised English water companies.