The Construction, Forestry, Mining and Energy Union's ACT secretary, Dean Hall, has accused two of the city's best-known construction firms of repeatedly using sham contractors to win government work.

He told a Legislative Assembly inquiry into procurement yesterday that Manteena and Iqon were undermining law-abiding Canberra companies by relying on subcontractors that underpaid their staff and avoided tax.

''I'll name [the sites] for you and I'll name the contractors who you're employing, because it's an absolute disgrace that the same contractors keep getting the same work.''

The two companies would not respond to the claims yesterday, which were made under parliamentary privilege.

Mr Hall cited Manteena's management of the construction of the Kingsford Smith School in west Belconnen, saying the 30 Chinese workers on the site were unskilled labourers working for plastering contractor Tilton.

They were owed $330,000 ''and they hadn't eaten in three days''.

For more on this story, see the print edition of today's Canberra Times.