Canada is joining the Trans-Pacific Partnership negotiations, a day after Mexico became part of the talks.
New Zealand's Minister of Trade Tim Groser says this week's developments demonstrate how dynamic the negotiation process is.
Together, TPP nations account for more than a quarter of world economic output, and Canada is the 11th country to join the proposed trade deal.
It is New Zealand's 17th largest goods trading partner overall, with total trade worth $1.2 billion in the year to March.
NZ-US Council executive director Stephen Jacobi says Canada's entry will increase pressure on the North American country to scrap the protection of its dairy industry.
"The continuation of supply management for dairy in Canada would appear to be incompatible with membership of TPP, so this has to be resolved somehow in the negotiation".
Canadian Prime Minister Stephen Harper says there's been no conditions attached to Canada's entry to the talks when asked if he would put supply management, which is a farm support programme, on the negotiating table.
But Mr Jacobi says New Zealand will expect the scheme to be all but scrapped.
"They would have to be able to contemplate significant market opening in the area of dairy products for this to be acceptable to New Zealand - how this is done, over what timeframe it is done and in what conditions is really a matter for the negotiation".
Canada joins Australia, Brunei Darussalam, Chile, Malaysia, Mexico, New Zealand, Peru, Singapore, the United States and Vietnam in negotiations to conclude a Trans-Pacific Partnership (TPP) agreement.