Hillary Clinton told manufacturers and union workers Monday that she'd fix "mistakes" relating to the North American Free Trade Agreement.

Campaigning in Pennsylvania for the Democratic presidential nomination, both Clinton and rival Barack Obama appeared separately and spoke at a summit sponsored by the Alliance for American Manufacturing in Pittsburgh.

Hillary Clinton, campaigning for the U.S. Democratic presidential nomination, speaks at the Sheet Metal Workers' Hall in Philadelphia on Monday.
(Matt Rourke/Associated Press)

Clinton told the audience her husband, Bill Clinton, erred when it came to the free-trade agreement with Canada and Mexico, which he signed in 1993 as U.S. president.

"As smart as my husband is, he does make mistakes," she said, promising to fix the deal or tell the two countries the United States is pulling out.

Earlier at the summit, Obama questioned Clinton's sincerity, charging that she has been two-faced about NAFTA since she has been a long-time supporter of the trade agreement.

The aim, he said, was to woo disgruntled workers, including those in Pennsylvania voting in next Tuesday's critical primary, who blame NAFTA for the loss of manufacturing jobs.

During her appearance, Clinton said that as New York senator, she commissioned a study to try to figure out what was going on with the flow of goods under NAFTA.

"There are so many layers of obstacles and barriers that are not really visible that prevent us from getting our goods into Canada, and I'm going to end that," she said.

Both Clinton and Obama have said they would threaten to dump NAFTA unless it's reopened to include protection for workers and the environment, but Canada opposed any renegotiation.

Clinton's trade pitch worked better than Obama's in struggling Ohio last month, after a leaked memo written by a Canadian Consulate official suggested Obama's rhetoric shouldn't be taken too seriously.

The Canadian government apologized, saying it wasn't an accurate reflection of comments from Obama's top economic adviser, Austan Goolsbee, who met with Canadian officials in Chicago in February.

With files from the Associated Press