Thirty illegal workers have been detained after a Department of Immigration and Australian Federal Police operation found them working on a construction site in Barton.
Department officers found one South Korean, one person from Hong Kong and 28 Chinese nationals when they raided the site yesterday.
Construction, Forestry, Mining and Energy Union ACT secretary Dean Hall said the workers were employed on the Hotel Realm site by The Doma Group.
Mr Hall said he had raised issues with Doma about subcontractors several times before the raid and the problem of illegal workers in Canberra was rampant.
''It's all over the place, there's mass exploitation, predominantly of Asians but also some from the Middle East,'' he said.
''It's quite sad because they think they are being employed legally ... and that they're going to be able to bring their families out eventually.''
The group will be transferred to Villawood Immigration Detention Centre, pending their removal from Australia as soon as possible.
Employers convicted under Commonwealth legislation face fines of up to $13,200 and two years' imprisonment while companies face fines of up to $66,000 per illegal worker. People with information about illegal workers or visa over-stayers are encouraged to call the Immigration Dob-In Line on 1800 009 623.