In a scathing letter to FAST, the BSA accused the group of "undermining what is an educational and supportive campaign" to encourage businesses to ensure their software licences are up to date.
Mike Newton, UK programme manager for the BSA, challenged FAST over the number of piracy cases it has pursued. "The issue is that FAST doesn't have the mandate," he said.
The BSA is a private company set up by software vendors, including Microsoft, Symantec, Adobe, Corel, Autodesk and Macromedia. Its mandate is to stamp out software piracy and recoup lost revenue for its members.
Recently the group sent out an "annual software audit return" to every UK organisation with 20 or more employees, asking them to complete a software survey.
"Where BSA and FAST differ is that FAST is an auditing company which charges a consultancy fee, whereas BSA, which represents the software publishers who write the licences, provides a self-audit tool for free," said Newton.
However, he admitted that only 20% of the 100,000 voluntary software audit returns were sent back to the BSA, and that only a few hundred of the 3,000 tip-offs the group receives each year are actively pursued.
Newton disputed FAST's contention that the software audit returns are used to help pursue punitive fines against companies that cannot produce valid software licences. However, he admitted the BSA checks against a company's self-audit form if a claim of software piracy is lodged through the group's hotline.
Despite the criticism, Richard Willmott, general manager of FAST corporate services, was sticking to his original statement. "If you receive a letter from the BSA, throw it in the bin," he reaffirmed to CW360.com.
"I cannot stress enough that membership of FAST is not immunity from prosecution," he added. "We actively prosecute companies that are reported to us as using, manufacturing and distributing illegal software irrespective of software manufacturer. Unfortunately, the BSA is concerned only with its members and is not a organisation actively educating users."
Willmott dismissed BSA claims that he belonged to an "auditing company", pointing out that FAST's charter forbids it from conducting audits.
Simon Moores, chairman of the Microsoft Users Forum, also reiterated his warning about the BSA's self-audit form. "What sensible managing director of a reputable UK company would sign an admission of guilt? It beggars belief," he said.
"Providing your company has its house in order, neither organisation can touch you," said Moores. "Piracy is a serious problem which damages our industry and we need to clamp down on it in a sensible way."
The deadline for returning the audit form is 30 November. "If a chief executive officer receives a letter from us, turns to the people responsible for IT and says this is a problem we should be addressing and then chooses not to return the audit, that is fine with us," said Newton.
However, he warned: "People who throw [the audit form] in the bin are burying their heads in the sand to what is a very significant problem."