Anti-piracy group the Business Software Alliance has come under fire from the Federation of Small Business and the Advertising Standards Authority.
The BSA recently sent out letters to 40,000 small businesses asking them to state if they had enough licences for their software.
The FSB slammed the letters as "reminiscent of the worst bogus directory and fake invoice scams."
It accused the BSA of misleading businesses into believing that giving information to the anti-piracy group is compulsory. John Harris, IT chairman of the FSB, advised small businesses to, "place this kind of correspondence where it belongs - in the bin."
The ASA has upheld a complaint from the Birmingham Chamber of Commerce about another BSA letter, which said that companies must reply or face having their details entered into a database of companies, "that we are concerned may be at risk of software mismanagement."
The Chamber of Commerce said the letter implied that it was official, and that the recipients were legally obliged to respond to it.
The ASA said that the letter did not warrant this official tone, as there was no evidence the companies targeted were using illegal software.
BSA campaign relations manager Mike Newton defended the organisation's approach, saying there was a correlation between BSA campaigns and a reduction in software piracy.
"The real aim of the campaign is to get companies to take action and check out their licensing," he said.
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