The SAC says that while the blacklisting was not "initially illegal", it was always "morally indefensible", and the companies involved continued to use it after it had become illegal.
The companies involved included some of the biggest names in construction but also many smaller firms.
The Blacklisting in Employment: Interim report, showed that The Consulting Association (TCA), an organisation set up to create, maintain and operate the blacklist, had been largely established by construction and engineering firm, Sir Robert McAlpine, which also provided TCA's chairmen for eight of its 16 years of operation.
It also found other major subscribers included Skanska and Balfour Beatty: the SAC has so far taken evidence from these three firms and intends to call more of those involved.
The blacklisting of building workers by large construction companies was a structure specifically set up to allow them to submit names and details of workers they deemed to be unsuitable to a central list.
The report states that as a result of this process, workers were denied employment without explanation, financial hardship was caused, lives were disrupted and sometimes ruined.
There was no right of appeal or challenge to the information held or the decisions made, and those affected, though they may have had their suspicions, had no evidence that they were being discriminated against in such a systematic and methodical way.
Ian Davidson MP, chair of the Scottish Affairs Committee said he was "appalled" by what was discovered during the hearings. "The Consulting Association was an organised conspiracy by big construction firms, to discriminate against workers who raised legitimate grievances over health and safety and other industrial issues," he said.
Davidson added: "This was an exercise run for the financial gain of the companies involved and those who benefited must be held accountable.
"We were neither convinced nor impressed by the attitude of the people involved in funding, operating and using this blacklist. The suggestion that this was somehow not a blacklist at all because people were not automatically refused employment if their name was on the list is ludicrous."
Unite, Britain's biggest union, has welcomed the report saying it has begun "to shine a light on the dark side of the construction industry."
Unite general secretary, Len McCluskey, said: "This is an industry that has ruined lives and discriminated against workers just because they belonged to a trade union or raised concerns about health and safety.
"We welcome the opportunity to give further evidence and recommend action against the blacklisters. Unite firmly believes blacklisting continues and the only way to eradicate this morally indefensible practice is to strengthen legislation against blacklisting to give the law real teeth.
He added: "There also needs to be a clear commitment to freedom of association and the right for unions to organise. Only then can we ensure that construction sites are safe workplaces free from discrimination."
Balfour Beatty said it had already acknowledged using TCA up until 2009 to carry out reference checks on employees in the construction industry.
In a statement a spokesman said: "We have expressed our genuine regret over this. It should not have happened and we have apologised to the workers and families who may have been adversely affected over the years by this."
The spokesman said the firm had undertaken steps to "address the shortcomings" revealed in its data protection practices, including a revised ethical code of conduct that was introduced in 2009.
The SAC says the Information Commissioner's Office, which raided TCA in 2009 and ultimately caused it to be closed down, should do more and work with the trade unions to locate and notify people that were on the blacklist, as they cannot begin to seek redress without this information
It has also appealed for further evidence as it enters the next phase of the inquiry before making recommendations to government.
