The Royal College of Nursing is seeking a judicial review of the vetting and barring scheme, which it says could breach nurses' human rights and undermine their ability to respond to patients' needs.
The scheme, developed in response to the murder of two schoolgirls by Ian Huntley and launched last October, is designed to prevent unsuitable people from working with children and vulnerable adults.
When it is fully operational, all nurses, midwives, nursing students and healthcare assistants will have to register with the Independent Safeguarding Authority, which can strike them off for up to 10 years if they are found guilty of certain offences.
The RCN argues that the scheme could breach the European Convention on Human Rights by denying nurses a fair hearing or a right to appeal. Its chief executive, Peter Carter, has now written to the Home Secretary, Theresa May, to inform her of his intention to apply for a judicial review.
A Home Office spokesman said Ms May would respond in due course and noted that last month's coalition agreement already committed the Government to reviewing the scheme and scaling it back to "common sense levels".
Dr Carter said: "Having had exhaustive discussions with the previous government over the inclusion of appropriate procedural safeguards for our members and having taken extensive legal advice, the RCN firmly believes the scheme is unfair."
Under the scheme, it is a criminal offence for individuals barred by the ISA to work or apply to work with children or vulnerable adults in a wide range of posts, including most NHS jobs.Reuse content