Three young men will challenge NSW Police in court after the force announced it will deny entry to anyone singled out by sniffer dogs at a Sydney festival this weekend.
Police warned this week that officers patrolling Saturday's Above & Beyond music festival at Sydney Olympic Park will kick out revellers targeted by the detection dogs.
"(We) will exclude any person from the venue that the drug dog indicates has or who has recently had drugs on them, regardless of whether drugs are located," NSW Police said on Facebook.
Tom Raue is one of three plaintiffs planning to file an injunction in the Supreme Court on Friday to stop what has been labelled an overreach of police powers.
Former commissioner of the Australian Border Force Roman Quaedvlieg, who spent more than three decades in drug enforcement, said he found the move "extraordinary".
"Festival drugs are risky granted but a person can have minute drug traces from handling cash, infused into garment fabric etc," he posted on Twitter.
Mr Quaedvlieg said the rates of positives and false positives can change depending on variables including the drug type and concentration, recency of contact, the crowd, the drug density and skill of the dogs involved.
"Using an 'indication', as they call it, to ban entry into a social event is too much," he said.
NSW Greens MP David Shoebridge said he had advice there was a strong case to be made that police do not have the power to follow through with their plan.
He claimed drug dogs can mistakenly react up to 75 per cent of the time.
"It's hard to see how this kind of action by police could be legal, seeing how it involves punishment in the absence of any offence," Mr Shoebridge said in a statement.
"This is nothing more than the NSW Police punishing young people for the abject failure of their drug dog program."
Australian Associated Press
