The largest U.S. labor organization said it will fight President Barack Obama on a free trade deal with South Korea, despite changes his administration made to the pact to broaden support.

The revised deal still fails to meet the AFL-CIO's requirements in areas ranging from workers' rights to currency manipulation, said Richard Trumka, president of the 12.2-million-member group.

"So long as these agreements fall short of protecting the broad interests of American workers and their counterparts around the world in these uncertain economic times, we will oppose them," Trumka said in a statement.

He also said the pact leaves open the possibility that goods produced in a North Korean industrial zone near the South Korean border could one day qualify for duty-free treatment in the United States.

The AFL-CIO has "grave concerns" over the North Korea's record on labor rights and the potential U.S. job losses that could result from competing against workers paid "perhaps the lowest wage levels in the world," Trumka said.

The statement foreshadows the battle that Obama can expect within his own Democratic Party as he pushes forward next year with his plan to ask for Congress to approve the pact.

Obama praised the trade deal in a speech to members of his export advisory council.

"It's an agreement supported by members of Congress on both sides of the aisle and Americans on all sides of the political spectrum, from the UAW (United Auto Workers union) to the Chamber of Commerce. And I look forward to working with Congress and leaders in both parties to approve it," he said.

The UAW has praised changes U.S. and South Korean negotiators made to auto provisions of the agreement in a marathon negotiating session last week.

The revisions also won strong backing from Ford Motor Co , which had been a vocal critic of the original pact.

White House spokesman Jen Psaki said Obama listened to all stakeholders, including labor, as he sought to strike a deal that "grows the economy and supports jobs here at home."

"The support of certain unions, including the United Auto Workers, plus Ford Motor Company, Democrats and Republicans and a broad group of business leaders has shown he made the right choice and that the final deal does just that."

Trumka acknowledged the new auto provisions would "give some much needed breathing room to the auto industry" and added the AFL-CIO appreciated the hard bargaining that was needed "to win these important changes."

"However, the labor movement's concerns about the Korea trade deal go beyond the auto assembly sector to a more fundamental question about what a fairer and more balanced trade policy should look like," Trumka said.

The United Steelworkers union said it also believed the revised agreement falls "far short of what is necessary to ensure that U.S. workers and businesses have a fair deal."

"We have concluded that, while improved, it still does not merit USW support, and we will oppose its passage," the union's executive board said in a statement. (Reuters)