From this:

A congressman is pressing the Department of Commerce to fully disclose a congressionally unauthorized plan to implement a trilateral agreement with Mexico and Canada that critics say could lead to a North American union.

Rep. Mike Rogers, R-Ala., chairman of the Subcommittee on Management, Integration and Oversight of the House Committee on Homeland Security, wrote July 11 to Secretary of Commerce Carlos Gutierrez requesting detailed disclosure of working groups in the Security and Prosperity Partnership office within his department...

He forwarded a letter from a constituent containing several good, detailed questions on their scheme. The questions are at the link.