Defence lawyers are challenging moves to establish a fixed fee regime for criminal legal aid, seeking a High Court injunction to stop the scheme's introduction in March.
The Criminal Bar Association has filed a judicial review in the Auckland High Court, claiming that the proposed changes are unlawful, unreasonable and invalid.
The association says while it accepts the need for the an efficient legal aid system, the proposed changes lack proper analysis and consultation.
A spokesperson, Matthew Goodwin, says by slashing funding for criminal legal aid cases, the Government is breaching the Legal Services Act and the Bill of Rights.
He warns the changes will lead to a two-tier system of justice - one for those who can afford to pay and one for those who can't.
Mr Goodwin says it will achieve the opposite of what was intended by the reforms recommended in the 2009 Bazley Report.
The case is expected to be heard on Thursday.