President Biden on Wednesday called for major increases to some tariffs on steel and aluminum products from China, speaking to members of a national steelworkers union in Pittsburgh as he vies with former President Donald J. Trump for votes in Northern industrial states.

“These are strategic and targeted actions that are going to protect American workers and ensure fair competition,” Mr. Biden told a crowd of about 100 union members at the United Steelworkers, which endorsed him last month. “Meanwhile, my predecessor and the MAGA Republicans want across-the-board tariffs on all imports, from all countries, that could badly hurt American consumers.”

The Biden administration has argued that a flood of low-cost exports from China is undermining American-made products — jeopardizing Mr. Biden’s push to expand U.S. manufacturing, a central focus of his economic agenda.

In his speech, Mr. Biden said he would ask the U.S. trade representative, Katherine Tai, to increase tariffs to what White House officials said would be 25 percent on certain Chinese products that now face tariffs of 7.5 percent, or none at all, pending the outcome of an administration review of the China tariffs initially imposed under Mr. Trump.

“I want fair competition with China, not conflict,” Mr. Biden said, flanked by supporters and signs that read, “President Joe Biden: Standing With Workers.” “And we’re in a stronger competition to win the economic competition of the 21st century with China or anyone else because we’re investing in America, and American workers, again.”

The move is another effort by Mr. Biden to put up new barriers to trade with China in some industries. It could help him compete with Mr. Trump in a “tough on China” context with swing voters, though administration officials said elections did not motivate the move.

A day earlier, Mr. Biden began a three-day swing through Pennsylvania, a crucial battleground state, by giving a speech in Scranton in which he focused on the tax code but repeatedly attacked Mr. Trump and accused him of favoring billionaires over the working class.

Mr. Biden’s plans on Chinese trade are more targeted than Mr. Trump’s, though. The former president has called for sweeping and steep new tariffs on imports from China and elsewhere, in a potential effort to fracture trade lines between the countries. Mr. Biden’s administration is reviewing existing tariffs and is expected to propose raising some rates on Chinese products while reducing others.

At a morning stop for breakfast on his way to Pittsburgh from Scranton, Mr. Biden was asked by reporters if he was worried about a trade war with China. “No trade war,” he replied.

Before Mr. Biden’s remarks, Ms. Tai announced that her office had begun an investigation into China’s aggressive support for shipbuilders and other related industries, in response to a union complaint.

“The American commercial shipbuilding industry is a shell of its former self,” the unions wrote in a filing with the trade representative. They added, “The biggest obstacle to the industry’s recovery is the unfair trade practices of the world’s largest shipbuilding nation: China.”

In the complaint, the unions cite “hundreds of billions” of dollars in Chinese government support for the shipbuilding industry. Those include supplying steel from government-owned companies at below-market rates, along with a variety of efforts to steer low-cost loans and other financing to shipbuilders from state-run companies. Ms. Tai called the allegations “serious and concerning.”

The moves threaten to deepen a trade dispute with Beijing, which has criticized Mr. Biden for his own efforts to subsidize American manufacturing — including tax credits in the Inflation Reduction Act that are meant to increase production of solar panels, electric vehicles and other technologies aimed at reducing fossil fuel emissions.

China’s Commerce Ministry sharply criticized the investigation in a release, saying it was “filled with a large number of false accusations, misinterpreting normal trade and investment activities as harming U.S. national security and corporate interests, and blaming China for its own industrial problems.”

In his speech, Mr. Biden also reaffirmed his support for the steelworkers union in a dispute over the proposed sale of the Pittsburgh-based U.S. Steel to Nippon Steel of Japan.

Nippon officials have vowed to invest billions in American manufacturing facilities, to keep U.S. Steel’s headquarters in Pittsburgh and to honor existing labor contracts. But the attempted purchase has drawn fire from the union and a bipartisan group of senators, largely from industrial states, who say it could compromise national security.

Mr. Biden has signaled opposition to the deal, which his administration is scrutinizing on security and antitrust grounds. He has said repeatedly that he will stand with steelworkers in the dispute over the sale, though administration officials have not specified exactly what that means in policy terms. In Pittsburgh, the president appeared to promise a worker that he would not allow the company to leave the United States — a move that no one is discussing currently.

“Let’s keep U.S. Steel in America,” one woman told Mr. Biden as he met with steelworkers before his speech.

“Guaranteed,” the president replied to cheers and applause.

David McCall, the international president of the steelworkers union, praised Mr. Biden before his speech.

“President Biden promised U.S.W. members that he had our backs,” Mr. McCall said. “And it’s clear he does.”

Mr. Biden and Mr. Trump are fighting for working-class votes in industrial swing states like Pennsylvania, Michigan and Wisconsin. Earlier on Wednesday, the Biden campaign released an ad featuring a steelworker promoting Mr. Biden’s economic record and attacking Mr. Trump.

This week, Mr. Trump’s case over falsified business records began in Manhattan, the first of the four criminal cases he faces to go to trial. Mr. Biden generally refrains from commenting directly on the trial. But his tour of Pennsylvania is meant to provide voters with a contrast to Mr. Trump’s legal troubles.

In his speech in Pittsburgh, Mr. Biden did take a veiled swipe at Mr. Trump, referring to him as “my predecessor, who’s busy right now.”

The crowd laughed, seeming to get the joke about Mr. Trump’s whereabouts, although the former president does not actually have to appear in court on Wednesdays.

Alexandra Stevenson contributed reporting.