Top officials from Canada, Mexico and the United States signed a fresh overhaul of a quarter-century-old trade pact on Tuesday that aims to improve enforcement of worker's rights and hold down prices for biologic drugs by eliminating a patent provision.

The signing ceremony in Mexico City launched what may be the final approval effort for U.S. President Donald Trump's three-year quest to revamp the 1994 North American Free Trade Agreement (NAFTA), a deal he has blamed for the loss of millions of U.S. manufacturing jobs.

The event at the Mexican National Palace was attended by Mexican President Andres Manuel Lopez Obrador, Canadian Deputy Prime Minister Chrystia Freeland, U.S. Trade Representative Robert Lighthizer, and U.S. White House adviser Jared Kushner.

"There is no question of course that this trade agreement is much better than NAFTA," U.S. House Speaker Nancy Pelosi said in announcing the agreement, saying the pact is "infinitely better than what was initially proposed by the administration."

U.S. President Donald Trump also hailed the deal.

Trump tweeted, "It will be the best and most important trade deal ever made by the USA. Good for everybody – farmers, manufacturers, energy, unions – tremendous support. Importantly, we will finally end our country's worst trade deal, NAFTA!"

The trade agreement, now called U.S.-Mexico-Canada Agreement (USMCA), was signed more than a year ago to replace NAFTA, but Democrats controlling the U.S. House of Representatives insisted on major changes to labor and environmental enforcement before bringing it to a vote.

The delay at times threatened to scuttle the deal, creating investment uncertainty in all three countries and worrying U.S. farmers already suffering tariffs stemming from Trump's trade war with China.

Intense negotiations over the past week among Democrats, the Trump administration, and Mexico produced more stringent rules on labor rights aimed at reducing Mexico's low-wage advantage. Both Canada and the U.S. House Ways and Means Committee said the deal included a mechanism for verification of compliance of union rights at the factory level in Mexico by independent labor experts.

Both the U.S. United Steelworkers union and the AFL-CIO labor unions endorsed the revised deal.

However, Mexico's chief negotiator Deputy Foreign Minister Jesus Seade said all disputes would be resolved through panels, and denied there would be anything like foreign labor inspectors in Mexico.

There was no immediate sign of the agreement being made public.

Some Mexican business groups fear that Lopez Obrador and Seade have ceded too much.

Gustavo Hoyos, president of employers federation Coparmex and a vocal Lopez Obrador critic, called the government "a bad negotiator." Other business groups focused on the positive and welcomed the looming end to months of uncertainty.

Seade himself said some of the changes were reasonable but not necessarily "good for Mexico".

(wiht input from Reuters)