Police arrested a 26-year-old woman who allegedly sprayed another female patron with a legally obtained canister during a fight at the Mayberry nightclub in Darwin early on Sunday.
At the same venue a week earlier, a 16-year-old allegedly attacked two bouncers with an unlawfully obtained spray after being denied entry.
The two incidents follow the September start of a 12-month trial allowing the public sale of pepper spray at select NT firearms retailers.
Western Australia is the only other Australian jurisdiction to allow general sale of the weapon.
NT Chief Minister Lia Finocchiaro previously said the move was part of justice reforms that would restore community safety and give people more tools to protect themselves.
During Sunday's incident, police arrested two women for fighting at the club after security separated the pair.
The older woman allegedly sprayed a 21-year-old, but a guard was able to "minimise the exposure" by smothering the canister's stream with his hand, police said.
Several people suffered minor effects from secondary contamination of the spray, while both women were charged.
Acting NT Opposition Leader Dheran Young said it was concerning legally obtained pepper spray was used in such a way and bystanders were affected.
"As an opposition we were calling out this trial quite early on, that weaponising people will only create more violence in the community," he said.
It was only a matter of time before someone was sprayed directly in the eye, risking potential blindness, Mr Young said.
The union representing security guards wants the spray trial scrapped.
United Workers Union NT secretary Erina Early said the scheme was dangerous for frontline workers such as security officers, paramedics, police and hospitality staff, describing the incidents as a "wake-up call".
"I think it's very irresponsible of this government to put out these weapons without actually considering what's going to happen to frontline workers," she told the ABC.
"It's not about empowering people at all, it's absolutely not - you're giving people weapons to hurt someone else."
Ms Early urged the NT government to meet with the union to discuss how to mitigate the risk from the weapons, which she said had been put on sale without consulting frontline workers.
Hospitality NT said swift work by security guards and police minimised harm during Sunday's incident.
"This sends a clear and unequivocal message that the misuse of any item as a weapon in a licensed venue will not be tolerated and will be met with the full force of the law," the industry body said in a statement.
"The fact that the item was legally purchased does not absolve an individual of the responsibility to use it lawfully and this incident demonstrates a clear breach of that responsibility."
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