Attorney-General Mark Dreyfus is again being urged to end the prosecution of a Tax Office whistleblower, with legal advocates warning the case will have a chilling effect on officials who witness wrongdoing.

Hearings related to the case of former public servant Richard Boyle will begin in the District Court of South Australia on Tuesday. He spoke publicly in 2018 about aggressive practices of the Australian Taxation Office, including hardline use of garnishee notices used to claw back tax debts from individuals and business.