The 90-day period would end August 16, 2017.
"This initiative presents a significant opportunity to update NAFTA in a way that will increase the export of more American vehicles and auto parts, and grow the number of high-quality and high-paying American jobs supported by such exports".
Still, Lighthizer said reforming the trade agreement fulfilled one of Trump's "key promises to the American people".
Trump made renegotiation of NAFTA a staple of his presidential campaign a year ago, asserting that the United States was at a disadvantage in trade with its northern and southern neighbors.
The split in Congress - which must approve any major overhaul of Nafta - mirrors a division in the Trump administration between traditional business-friendly Republicans and the economic nationalists who frequently join with liberals in calling for measures at the border to protect American workers from unfair competition.
Canada Foreign Affairs Minister Chrystia Freeland said many USA jobs depend on NAFTA which has created growth throughout the region.
Lori Wallach, director of the Public Citizen's Global Trade Watch, says NAFTA needs a complete overhaul. "Better for the people of Mexico, the people of the US and the people of Canada". That follows on the heels of disputes with Canada over lumber imports and dairy exports, and with Mexico over sugar imports, just a small sample of the many trade disputes announced in the last three months.
There were reports in April that Trump was considering an executive order to withdraw the us from NAFTA. Washington's current political upheaval - and Mr. Trump's trade-related threats to neighbors - could also derail a deal.
Secretary Tillerson told reporters there is much more to the U.S. Mexico dynamic than NAFTA and "the wall does not define our relationship".
U.S. Commerce Secretary Wilbur Ross says he is putting Congress and trading partners on notice that "free and fair" trade is the new standard in the U.S.
U.S. Trade Representative Robert Lighthizer's letter to Congress is far from belligerent. But the pact did encourage American manufacturers to relocate some operations to Mexico to take advantage of cheaper labor there; critics blame NAFTA for wiping out US factory jobs. "We are committed to working with the Canadian Government on this issue and will strongly represent the interests of the produce industry during any renegotiation process", said Lemaire.
When the US and Mexico made the free-trade deal in the 1990s, negotiations went on for more than a year. Nowhere is the importance of trade stronger than right here in North America.
"I want to be optimistic because I think it's important that we get a good agreement", Hoback said.