Trump has warned he could proceed with a deal with Mexico alone and levy tariffs on Canada if it does not come on board - US lawmakers have said ratifying a bilateral deal would not be easy.
Guajardo suggested that disputes over currency transparency could play out under Nafta’s Chapter 20 state-to-state settlement process.
The US Chamber of Commerce, Business Roundtable and National Retail Federation were calling for a deal with both countries rather than separate pacts, as President Donald Trump suggested.
Prior to Monday’s announcement, the Trump administration had been threatening tariffs of as much as 25% on vehicles imported from any country.
Canada and the EU provisionally entered into a free trade pact last September, as Nafta appeared to falter and the US exited from the Trans Pacific Partnership.
Trump said he would drop the name Nafta from the accord because of its unpopularity.
Significant breakthroughs between Mexico and the US came during the past several days on the contentious issues of automobiles and energy.
Representatives from US and Mexico are now discussing a periodic review process that spares the Nafta from automatic expiration unless new terms were agreed.
Mexico's Economy Minister Guajardo declined to go into detail on the topics remaining with the US but said the agreement could happen at any time.
NAFTA and China have been key targets of US President Donald Trump's aggressive trade strategy, largely brushing off business community concerns about harm to the US economy.
Foreign brands with smaller North American manufacturing footprints and fewer US research and development staff may have difficulty meeting more stringent content requirements.
The US-Mexico talks resumed in July, without Canada, after negotiations involving all three members of the US$1.2 trillion trade bloc stalled in June.
Trump has said recently he might prefer to end the decades-old Nafta pact in favour of inking separate, bilateral agreements with the US’s southern and northern neighbours.
While cautioning that he was “not a negotiator’’ involved in the talks between the US, Mexico and Canada, Hassett said his colleagues who are renegotiating the deal have indicated things are going well.
NAFTA talks between the US, Mexico and Canada had stalled since June when the US slapped tariffs on Mexican and Canadian steel and aluminium.
The letter states that the incoming administration's aim is to "start a new chapter in the relationship between Mexico and the United States, based on mutual respect."
Mexico depends heavily on trade with the United States, which receives about 80% of its exports.
Lopez Obrador, who will take office in December, said he would discuss NAFTA with President Enrique Pena Nieto in their first meeting after the election, set for Tuesday.
In the past, General Motors has received criticism for similar moves.
Navarro on Sunday joined administration officials in lashing out at Trudeau following the chaotic end to the G7 summit in Quebec where leaders of the world's major economies clashed over tariffs.
Although Canada and Mexico say the idea is unworkable, Trump told reporters earlier on Saturday that the new deal would contain such a provision. Trudeau rejected the idea.
The top Nafta negotiators from the US and Canada met earlier during the summit, after Trump in the morning complained about what he called unfair trading.
Canada, Mexico, and the United States have been holding talks to revise NAFTA since August 2017.
Merkel is due to address contentious issues including trade when she meets Trump on Friday.