BUILDING firms using illegal immigrant workers will be blacklisted and suspended from bidding for government contracts, it was announced yesterday. Under the new ruling from the Works Branch, any contractor convicted more than twice within a 12-month period of hiring or allowing illegals to work for them will face being suspended from the approved list of companies that are allowed to compete for government work. The six-month suspension applies to contractors convicted of using the illegal workers on public or private works projects and will take effect from the date of the last conviction. Contractors who are already in the process of bidding for tenders for public works programmes will also be liable to be placed on the blacklist if they are convicted of employing illegals. A Works Branch spokesman said: ''The new measure is in line with the Government's policy to tackle the problem of illegal immigration effectively.'' The Housing Authority announced a similar ban in January on contractors bidding for its works. The Secretary for Works, Mr James Blake, has informed the Hongkong Construction Association that the ban will come into force before the end of the month.