Making returning New Zealanders pay for managed isolation would "disproportionately" affect lower-income families based overseas and could be "a breach of fundamental rights", an advocacy group says.
The Government has said charging people for their managed isolation stay is on the cards, while The National Party has promised to implement it if elected in September.
Prime Minister Jacinda Ardern said last week the Government was working through a payment scheme but it wanted to make sure the quarantine system itself was working properly first.
A group called Team of 6 Million, made up of 14 overseas-based Kiwis "united against quarantine fees", say many people in isolation have suffered "terrible losses" with no choice but to return to New Zealand.
"This user-pays approach would disproportionately affect low-income Kiwis based overseas, and could well be a breach of New Zealanders' fundamental rights as well as a violation of Māori rights to tino rangatiratanga under Article 2 of Te Tiriti o Waitangi," spokesperson Phoebe Carr said.
"We have heard numerous stories of people who have suffered terrible losses - be they employment opportunities or the death of a loved one - who now find themselves making the stressful transition from their current country of residence back home to New Zealand."
Minister in charge of managed isolation Megan Woods said on Wednesday a final decision about making people pay for quarantine facilities hadn't been made.
The Opposition, meanwhile, has promised to charge adults $3000 each.
"National won't expect taxpayers to pay for other Kiwis returning from high-paying careers or expensive holidays in Europe," said Gerry Brownlee, the party's COVID-19 spokesperson, and deputy leader.
But Team of Six Million says many Kiwis have been faced with an "insurmountable task" of getting home.
"Our view is that New Zealand should retain its publicly-funded quarantine system," spokesperson Max Harris said.
"A system without exemptions is simpler and less costly to administer, so our position is no quarantine fees: no caveats, no ifs or buts."
The group has launched a petition calling for no quarantine fees, which has amassed nearly 3600 since Wednesday.