A bill before Parliament seeks to put the peddlers of synthetic drugs behind bars for longer.
The Psychoactive Substances Amendment Bill, which would increase the maximum jail time for supplying synthetic drugs from two years to eight years, passed its second reading in Parliament last week.
National and New Zealand First supported it, while Labour, the Greens and Act opposed.
But NZ First justice spokesman Darroch Ball said his party's ongoing support depended on National backing an amendment to boost the maximum prison sentence to 14 years, in line with penalties for Class B drugs such as morphine, opium and ecstasy.
The move comes at a time when many are questioning whether a punitive approach to curbing illicit drug use actually works and as an increasing number of countries are relaxing drug laws, especially when it comes to cannabis.