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 Gord