Some of the Tongans are now permanent residents.
Of the 245 Chinese students who arrived on fraudulently obtained visas, 56 have left but 154 have become unlawful.
Association chairman Walter Stone said: "We do not think New Zealand can afford the cost of deportation."
Overstayers from five Pacific countries - Samoa, Tonga, Fiji, Tuvalu and Kiribati - make up 7504, or 53 per cent of those unlawfully here, and estimates also show significant increases in overstayers from India and Kiribati.
China is the source of 1604 overstayers, India 678, Great Britain 506, Malaysia 447 and South Korea 354.
"Unlawful immigrants have a highly negative impact on the economy and society, and they bring legitimate migrants into disrepute," Mr Stone said.
"Further, unlawful migrants are exploited in the workplace by unscrupulous employers which means employment is taken from New Zealanders and legitimate migrants."
Most overstayers, or 62 per cent, previously held a visitor visa, while 2345 had been on a work visa and 1808 on a student visa.
People who are deported face a ban on returning and are required to pay the cost of their deportation before they can be considered for a visa, said Immigration fraud and compliance manager Peter Elms. In the past five years, the agency managed to recover only about 10 per cent of the cost from the 3918 it deported.
Mr Elms said the agency was now focused on encouraging overstayers to depart at their own cost.
"Voluntary departure enables the individual to co-operate with Immigration, settle their affairs and pay for their own costs in returning to their home country," Mr Elms said.
Last year, there were 1393 voluntary departures compared with 767 deportations, up from 842 in 2008 and 1163 in 2011.
Mr Elms said the Crown would still meet the cost for those unable to pay their own way.
