Postal workers have been urged to make official requests for any information held about them if they suspect their names were kept on a "blacklist" of thousands of workers.
The secret file of over 3,200 mainly construction workers was uncovered in 2009 after a raid by the Information Commissioner's Office (ICO) on the Consulting Association.
Workers were included on the blacklist for raising health and safety concerns on building sites, or merely for being union activists, and were often denied work for years as a result.
It has recently been revealed that other workers, including firefighters, teachers and postal staff, also had their details included on the blacklist.
Dave Smith, of the Blacklist Support Group, told the annual conference of the Communication Workers Union, that postal workers should contact the ICO if they suspected their names were on the blacklist.
"People in this hall will definitely have been spied on by undercover police," he told the Bournemouth conference.
The price of first and second class stamps is to increase by 1p each to 63p and 54p from March 30, the Royal Mail announced today.
Sending a large letter will increase by 2p to 95p for first class and by 1p to 74p for second class.
Second-class medium parcels weighing up to 2kg will be priced at £4.89, which Royal Mail said represents a saving of up to £3.11.
The postal group said it had thought "carefully" about the impact on its customers before deciding to raise letter prices, adding that it recognised how the recent tough economic conditions had made it difficult for consumers and businesses.
Stamp prices in the UK were among the best value in Europe, it added.
The man who oversaw the controversial privatisation of Royal Mail will be stepping down later this year, the postal firm has announced.
Chairman Donald Brydon, who has been in the post since 2009, will continue work until at least the annual general meeting in the summer, but a statement from the company revealed the search for his successor had already begun.
I am proud of what Royal Mail has achieved as a company in the last six years.
Our transformation is well underway and we are now a FTSE 100 listed company. I feel that now is the right time for me to make this decision.
Business Secretary Vince Cable has accused the boss of Royal Mail of "scaremongering" in claiming the universal post service is under threat.
Chief executive Moya Greene has warned that the high cost of the service, which ensures a same-price delivery for letters anywhere in the UK, six days a week, is not sustainable in the face of competition in high-density, low-cost areas.
ITV News business editor Joel Hills reports:
Business Secretary Vince Cable has criticised Royal Mail bosses for “scaremongering” by indicating universal service may be under threat.
He said he felt it was "wrong" of chief executive Moya Greene to suggest it is.
He said a lot of people “depend” on the Royal Mail and the regular delivery it provides, particularly in remote areas, and he said they should not be made to feel insecure.
I think it’s wrong to scare the public.
The universal service obligation is absolutely clear, it’s protected in law by Parliament, it’s not going to change.
I think a bit of scaremongering is going on and it’s not healthy.
The privatisation of Royal Mail has gone “admirably” but the biggest competition to business was always going to be the ever-growing popularity of email, Vince Cable has said.
The Business Secretary told ITV News that the major objective of privatisation had been to allow Royal Mail to go out and compete and raise money on the open market for investment, which it had – raising £500 million to date.
But, he said, they were always going to have to compete with e-mail, which was replacing much of its traditional custom, on top of having to compete with other mail carriers.
Business secretary Vince Cable has accused Royal Mail bosses of "scaremongering" by claiming the universal service is under threat.
He told ITV News the universal service obligation - which ensures people can send post anywhere in the UK for the same fixed price - is enshrined in law and will not be rescinded.
He said were it to be overturned, both Houses of Parliament would have to vote to do so - which, he added, is not going to happen.
It comes after Royal Mail chief executive Moya Greene warned that increasing competition in high density, low cost areas was threatening the universal service by making delivering to rural and remote areas not economically viable.
Mr Cable said Royal Mail, now it is only 30 per cent owned by the taxpayer, was free to raise capital privately - and said it had already raised £500 million to invest and compete.
He said the government did not want to see companies "whinging" about having to operate in a competitive market.
Business Secretary Vince Cable has accused Royal Mail of "scaremongering" over warnings it may not be able to continue with its universal service.
Mr Cable told ITV News that chief executive Moya Greene's comments amounted to "special pleading" - and said the government did not want companies "whinging" about being in a competitive market.
ITV News Business Editor Joel Hills tweeted:
Vince Cable accuses Royal Mail of "scaremongering" over the threat to the universal service. 30% of the company is still taxpayer owned.
Vince Cable tells @itvnews Royal Mail is operating in a competitive market and "we don't want, frankly, people whinging about it."
"It's wrong to scare the public". Vince Cable says a lot of people depend on the Royal Mail. "They should not be made to feel insecure".
Royal Mail bosses today issued a warning that giving people more choice between delivery services was threatening the future of the universal service, which guarantees that letters can be delivered anywhere in the country for the same price.
Chief executive Moya Greene told a committee of MPs that the high cost of the universal service obligation – around £7.2 billion a year – was in part because of the difficulties of delivering to rural and remote parts of the country.
Delivering to high-density areas such as the inner city was much lower cost and helped to subsidise these deliveries – but by allowing these customers to “cherry pick”between Royal Mail and their competitors the system was unsustainable.