The Inland Revenue would not comment but the letter makes it clear that it will go through contractors' tax records from the past year looking for evidence of tax evasion, bogus self-employment and fraud.
The letter says that if the Inland Revenue does find evidence of such illegal practices it will prosecute. It is understood that the compliance unit will be based in Newcastle upon Tyne.
The move comes amid growing concern that the number of bogus self-employed in the industry is rising, despite the introduction in 1999 of CIS cards to tackle the problem.
At the time many subcontractors were paid gross of tax. The new scheme introduced more stringent tests, tax certificates and registration cards. Employers have been required to see CIS cards before making gross payments since the introduction of the scheme. However, unions have criticised the scheme, claiming that contractors classify individual workers as self-employed to avoid paying national insurance contributions.
A source in one industry board confirmed that action was needed. He said: "Initially there was a move by construction firms to employ more direct labour. But this trend has been completely reversed as it has become apparent there has not been a clampdown. We desperately need some prosecutions."
Bob Blackman, T&G general secretary for construction, said the clampdown was welcome and a clear sign that the Inland Revenue was genuinely interested in seeing a change.
The move follows claims by UCATT general secretary George Brumwell in August that chancellor Gordon Brown had promised a review of bogus self-employment in the industry.
It is apparent that there has not been a clampdown. We desperately need some prosecutions
Industry body source
Union concerns over bogus self-employment centre on the loss of employment rights. If a worker is deemed to be self-employed, he or she loses benefits such as redundancy and holiday pay.
Unions argue that the problem is the result of too many CIS cards, a legal requirement, being issued.
The revenue's compliance unit must now monitor contractors more closely and check that employees are genuinely self-employed.
The Inland Revenue is also concerned about bogus self employment because it enables contractors to avoid paying the employer's national insurance contribution of 12% of salary. The unions claim this money could be used to redevelop the industry.
A spokesperson for the Inland Revenue said that it did not discuss individual compliance units and working practices.
