WELLINGTON (TIP): The Trans-Pacific Partnership, one of the world’s biggest multinational trade deals, was signed by 12 member nations on Thursday in New Zealand, but the massive trade pact will still require years of tough negotiations before it becomes a reality.

The TPP, a deal which will cover 40 percent of the world economy, has already taken five years of negotiations to reach Thursday’s signing stage.

The signing is “an important step” but the agreement “is still just a piece of paper, or rather over 16,000 pieces of paper until it actually comes into force,” said New Zealand Prime Minister John Key at the ceremony in Auckland.

The TPP will now undergo a two-year ratification period in which at least six countries – that account for 85 percent of the combined gross domestic production of the 12 TPP nations -must approve the final text for the deal to be implemented.

The 12 nations include Australia, Brunei, Canada, Chile, Japan, Malaysia, Mexico, New Zealand, Peru, Singapore, the United States and Vietnam.

Given their size, both the United States and Japan would need to ratify the deal, which will set common standards on issues ranging from workers’ rights to intellectual property protection in 12 Pacific nations.

Opposition from many US Democrats and some Republicans could mean a vote on the TPP is unlikely before President Barack Obama, a supporter of the TPP, leaves office early in 2017.

US Trade Representative Michael Froman has said the current administration is doing everything in its power to move the deal and on Thursday told reporters he was confident the deal would get the necessary support in Congress.

In Japan, the resignation of Economics Minister Akira Amari – Japan’s main TPP negotiator – may make it more difficult to sell the deal in Japan.