United States Democratic presidential candidate Hillary Clinton has come out swinging against the Trans-Pacific Partnership Agreement (TPPA).
Twelve Pacific Rim countries including New Zealand reached an agreement on the deal on Tuesday after years of gruelling negotiations and a "brutal" final push in Atlanta.
The secretive deal has removed tariffs for 93 percent of New Zealand's exports, with taxes remaining on beef exports to Japan and on dairy.
It is estimated it would be worth $2.7 billion a year to New Zealand's economy by 2030.
While the deal has been agreed to, it still has to make it through each respective country's parliaments.
If it is passed, it will become the biggest trade deal in history, representing 40 percent of the world's GDP.
There has been vocal opposition to the TPPA from many countries including New Zealand, Canada, Japan and the US.
And Ms Clinton added her voice to that on Wednesday (local time), telling PBS on the campaign trail that "as of today, I am not in favour of what I have learned about it".
"I have said from the very beginning that we had to have a trade agreement that would create good American jobs, raise wages and advance our national security and I still believe that is the high bar we have to meet.
"I don't believe it’s going to meet the high bar I have set."
She said she was worried currency manipulation was not part of the agreement and that "pharmaceutical companies may have got more benefits and patients fewer".
Earlier this year, Congress granted President Barack Obama 'fast-track' authority to negotiate trade deals. Although Congress will be able to approve or reject agreements, it won't have the power to change them.
It is seen as one of Mr Obama's legacy policies.
The TPPA faces stiff opposition in the US Congress, which has 90 days to review the agreement before voting on it.
However, under the President's new powers, the deal only needs a majority vote rather than the 60 votes required in the US Senate.