But Lighthizer said that "for countless Americans, this agreement has failed".
The flow of Alberta oil into the U.S.is not likely to become an issue as the first round of NAFTA renegotiations get underway, according to a Calgary trade analyst.
Lighthizer, meanwhile, lamented the US trade deficit with Canada. "I want to be clear that he is not interested in a mere tweeking of a few provisions and a couple of updated changes".
In a tough opening speech to kick off this week's talks, US Trade Representative Robert Lighthizer highlighted the importance of modernising the deal to acknowledge the growth of the digital and service sectors in the 23 years since NAFTA was signed.
The Office of the United States Trade Representative published the letter sent by Ambassador Lighthizer to congressional leaders.
Lighthizer put Mexico and Canada on notice that the United States would use its clout as their biggest export customer to wring concessions, saying the United States wanted substantially tougher rules of origin, including a requirement of "substantial USA content" for autos. "That is par for the course in any trade negotiation and the Canadian approach remains one of confidence based in strength".
Lighthizer's rhetoric contrasted with the tone of his Mexican and Canadian counterparts, who emphasized the gains to all sides of the original deal.
The top US trade negotiator says Americans have lost more than 7,000 jobs.
Trump congratulates Curtis on unofficial GOP win
Bob Bennett, a longtime Republican who lost re-election in 2010, the first of several GOP candidates ousted in tea party wave. In addition, the fall contest will be complicated by the insurgent candidacy of Jim Bennett, son of the late three-term Sen.
Those comments were in stark contrast to those by Canadian Minister of Foreign Affairs Chrystia Freeland and Mexican Secretary of Economy Ildefonso Guajardo Villarreal, who stressed the pact brought benefits for all three economies.
The tri-lateral agreement removed most tariffs between the U.S., Canada and Mexico but the Trump administration says the deal only encouraged manufactures to move south of the border to take advantage of lower wage Mexican labor. It settles complaints about illegal subsidies and dumping and has often ruled against the U.S. Trump wants it gone - but Canada says it will walk away from the table if the U.S. pushes for its removal.
"We are looking for a constructive process that will take NAFTA into the 21st century", he said.
He emphasized the importance of the three countries taking a regional perspective in the negotiations, saying that the agreement was about "shaping a common vision of North America".
Guajardo said "NAFTA has been a strong success for all parties" and can not be improved by "tearing apart what has worked".
"For a deal to be successful, it has to work for all parties involved, otherwise it's not a deal", Guajardo said. Trump has been so opposed to NAFTA and the Trans-Pacific Partnership that having prior experience with trade agreements is often viewed as a political liability for potential appointments, they said.
"You should expect the bravado in public statements before negotiations begin", said Goldfeder.