Kiwifruit growers pay a 45 per cent tariff which will be phased out over five years and avocado growers a 30 per cent tariff which will be phased out over nine years.
The agreement was signed in Seoul this week and as soon as it is passed it will eliminate tariffs of $65 million a year on goods which at present are forced to pay tariffs of $229 million a year. Within 15 years 98 per cent of tariffs will go.
The attacks on Mr Peters came from Mr Key in South Korea, Finance Minister Bill English, Economic Development Minister Steven Joyce, and Environment Minister Nick Smith in Wellington, and National candidate Mark Osborne in Northland.
Dr Smith said that having worked with Mr Peters previously in Government he found him "Machiavellian."
"He is hard work and unpredictable and there in no questions that if Winston wins the Northland byelection, resource management reform will be more difficult."
Mr English and Mr Key suggested that a private members bill before the House sponsored by New Zealand First MP Fletcher Tabuteau could scuttle existing FTAs including the Korea deal if Mr Peters wins Northland and brings in another list MP.
"If they elect Mark Osborne, there will be no trouble about it going through. If they elect Winston Peters they are taking a punt."
But the Korea FTA is not under threat. The NZ First bill, which bans any Government from entering free trade agreements with an investor-state dispute settlement procedure (ISDS) including the Korean FTA, is opposed by National, Act's David Seymour and United Future's Peter Dunne with 61 votes combined.
That is enough to scuttle the bill either before or after the byelection to vote the bill down at its first reading on May 6.
But Mr English said that showed Mr Peters was saying one thing in Northland and yet in Wellington was supporting laws that moved in the opposite direction.
Labour leader Andrew Little clarified earlier statements to reporters suggesting his party would vote against any trade deal containing an ISDS -- which would include the Korea FTA.
"I may have somewhat overstated the issue," he told the Herald.
He said Labour's objection to ISDS was when they were used indiscriminately. Labour had put an ISDS clause in the free trade agreement with China but where two developed countries had faith in each other's judicial system, there was no need for it.