ASIO will have unfettered powers to brand refugees a security risk to Australia under a Coalition government - condemning more than 50 people presently held in detention to a legal black hole.

Refugees given a negative assessment by the security agency will lose their only form of appeal to the secret finding, with the Coalition pledging to scrap a review introduced by Labor last October for a retired judge to examine their case. ''I also do not believe that ASIO rulings should be reviewable,'' chief opposition whip Warren Entsch said in a letter responding to a campaign urging the release of refugees held with the adverse assessments. ''The current processes that ASIO go through are already incredibly sensitive and we rely on them absolutely.''

The plan to abandon the review process would enshrine a form of indefinite detention for people judged to be refugees but not permitted release into the community.

The highest profile of these detainees, Tamil woman Ranjini, gave birth to a child last month and remains locked up in Sydney with her other two young boys. Ranjini had lived freely in Victoria for a year until last May before ASIO made its determination and she was incarcerated. She is not permitted to know the reasons for the adverse assessment, but it is believed to involve her former husband, a driver with the separatist Tamil Tigers who was killed during Sri Lanka's civil war.

Several Tamil refugees have been held for more than three years since arriving in Australia, with self-harm common among the group.