The ACT Party leader says he tried to change the National Party's mind on animal testing for legal highs but was unsuccessful.
Parliament has advanced legislation to introduce a regulatory regime for party pills and synthetic cannabis, with some restrictions on animal testing.
The bill will require manufacturers to use options other than animal testing to prove their products are safe, if they are available.
A Green Party attempt to effectively block animal testing for legal highs sold in New Zealand was defeated on Tuesday night.
The proposed ban was wholeheartedly supported by ACT's John Banks, who says he failed to convince National to come on board.
The Greens say Mr Banks should have used his position as National's confidence and supply partner to push the case harder.
However, Mr Banks says he has spoken to the National Party both publicly and privately and has been unable to sway their decision.
Mr Banks has challenged the Green Party to withdraw its support for the legislation now the amendment has failed.