By Victoria Bone
Union say those who question health and safety can be targeted
An investigation by the Information Commissioner says it has uncovered a secret database of building workers.
The Commissioner says notes on individuals - including descriptions such as "ex-shop steward, definite problems" and "Irish ex-Army, bad egg" - were used to unlawfully vet job applicants.
The BBC News website spoke to two workers who say this alleged "blacklisting" is not new and can be very damaging.
It often happens, they say - and unions agree - to those who are simply trying to make their industry safer by raising concerns over health and safety.
Arthur McKevitt described his experience in 1987 when he lost a lucrative opportunity to work on the building of the Channel Tunnel because he had been blacklisted.
He said: "Half way through my induction one of the chaps in charge came over and said, 'You can't start today, you'll have to come back tomorrow.'
"I thought something wasn't right and the next day he said I couldn't work for them because I had been branded a troublemaker.
"The only thing I could think of was that a few years before I had a job in the north east of England and there were a lot of health and safety problems.
"There were a few arguments with the management over it."
Mr McKevitt, now 66 and living in Newry, County Down, refused to accept the decision.
His data was being held by an organisation called The Economic League which gathered information on workers who could be deemed to be subversive or had particular associations such with the Communist Party.
Mr McKevitt attempted to sue The Economic League, but it placed itself into liquidation before the case came to court.
He was eventually able to clear his name, but suffered a lot in the meantime.
"It was very damaging to me," he said. "I lost a year and a half of work. I would say I spent £10,000 on the case, as well as all the lost wages.
"This is a disgusting practice. It clashes with the rule of law."
Roddy Kyle was another worker who believes he experienced blacklisting in the 1980s, again because he raised safety concerns.
He is a mechanical engineer, specialising in work on oil rigs, and his problems began after the Piper Alpha rig disaster in 1988 in which 167 people died.
"It was glaringly obvious that the platform had blown up due to very, very lax safety measures," he said.
"Piper Alpha was an accident waiting to happen and the majority of workers knew that, but they wanted their jobs as well. It was a very difficult time to get work so if you got a job you sat tight.
"But I have always been very strong on safety. It's a dangerous industry and you have to keep your wits about you.
"So if there are any problems I've always been outspoken about them, but I've always raised real issues, not spurious ones."
In 1989, Mr Kyle, now 66 and living in Inverness, was involved in investigating several accidents on the Shell Tern platform in the North Sea.
Shortly afterwards he was told he was being replaced, supposedly because he "wasn't prepared to get on with fellow workers".
He was then moved to another platform - after fighting against a pay cut - where he again made complaints about health and safety.
Soon after that he was sacked - in his view because he had been branded as someone who would not keep quiet.
Mr Kyle took his case to an employment lawyer and eventually accepted a £10,000 settlement.
"It was a very difficult period, not one that I really want to remember," he said.
"It was common knowledge that blacklisting went on - companies want to be able to get to the end of a job and say it's been completed on time, on budget and without any safety incidents.
"But it's often not true, there are problems going on behind the scenes.
"The thing is you are not just putting your head above the parapet at one firm, you're doing it across the industry and you could be putting your whole future career at risk."
The Union of Construction, Allied Trades and Technicians (Ucatt), said many of its members, some of them designated onsite safety representatives, had been "victimised and dismissed after complaining and whistle blowing about dangerous sites".
General Secretary Alan Ritchie told the BBC: "Really, in the 21st Century, do we need this sort of McCarthyism?
"Simply because you were prepared to turn around and say, 'By the way, the health and safety in this site is a disgrace and there's got to be something done about it,' suddenly you find yourself never working in the industry for years."
Ucatt pointed out that construction is the most dangerous industry in Britain, with more than 70 deaths last year.
It says the use of blacklisting against those trying to change that could have serious safety implications.