WASHINGTON (AP) -- Making good on a campaign promise, the Trump administration formally told Congress Thursday that it intends to renegotiate the North American Free Trade Agreement with Canada and Mexico.

U.S. Trade Rep. Robert Lighthizer sent a letter to congressional leaders Thursday, starting 90 days of consultations with lawmakers over how to revamp the pact. Talks with Canada and Mexico can begin after that.

The two-page letter offered few details about what changes the administration would seek in the 23-year-old pact that President Donald Trump has called "a disaster." Lighthizer told reporters that any new deal should do a better job of protecting U.S. factory workers and should be updated to reflect new technologies.

Last month, White House aides spread word that Trump was ready to pull out of NAFTA. Within hours, the president reversed course and said that he'd seek a better deal first.

"We are going to give renegotiation a good strong shot," Lighthizer said. He refused to say whether leaving NAFTA remained an option.

The trade agreement has dramatically increased trade among the three countries. American farmers have mostly benefited from the reduction in trade barriers. But the pact encouraged American manufacturers to relocate some operations to Mexico to take advantage of cheaper labor there; so critics blame NAFTA for wiping out U.S. factory jobs.

"Since the signing of NAFTA, we have seen our manufacturing industry decimated, factories shuttered, and countless workers left jobless," Commerce Secretary Wilbur Ross said in a statement. "President Trump is going to change that."

In March, the administration circulated an eight-page draft letter on NAFTA that disappointed critics by appearing to keep much of the existing trade agreement in place.

In advance of renegotiations, the administration has sparred with Canada over inexpensive Canadian timber and Canadian barriers to U.S. dairy products. Lighthizer said he hoped those disputes could be resolved separately from the NAFTA talks.