Harris campaign spokesman James Singer said the move would be part of "a fiscally responsible way to put money back in the pockets of working people and ensure billionaires and big corporations pay their fair share".
When Trump was president, he slashed the corporate tax rate to 21 per cent from 35 per cent and implemented other tax breaks that are set to expire next year.
Trump has vowed to make the cuts permanent.
Changes to the US tax code require approval by Congress.
Democrats and Republicans are in a tight battle for control of the Senate and the House of Representatives, both up for grabs in the November 5 election.
Harris, a Democrat, has pledged to maintain US President Joe Biden's promise not to raise taxes on people who make $US400,000 ($A594,200) or less a year.
In an economic policy speech last week, Harris outlined proposals to cut taxes for most people in the US, ban "price gouging" by grocers and build more affordable housing as part of the "opportunity economy" she plans to pursue if she wins the White House.
Trump pledged on Monday to rescind a Biden administration rule limiting power plant pollution and reiterated a promise to block Nippon Steel's planned purchase of US Steel.
"I will stop Japan from buying United States Steel," Trump said. "They shouldn't be allowed to buy it."
Donald Trump says he would "issue rapid approvals for new energy infrastructure" as president. (EPA PHOTO)
In the most detailed economic remarks he has offered on the campaign trail so far, Trump also ratcheted up his pledge to radically limit foreign access to domestic markets, saying he would ensure the supply chain for essential goods would be 100 per cent American if he wins the November 5 election.
He did not elaborate on how he would accomplish that goal beyond advocating broad measures, like imposing tariffs on other nations.
US Steel said in a statement after Trump's remarks that it is "committed to the transaction with Nippon Steel, which is the best deal for our employees, shareholders, communities, and customers."
The former US president spoke to a crowd of supporters on a factory floor in the working-class city of York, Pennsylvania.
Biden in March said it is vital for US Steel "to remain an American steel company that is domestically owned and operated".
Trump also pledged to eliminate rules published by the Environmental Protection Agency in April, which limit air and water pollution from power plants and are designed to cut over one billion metric tonnes of greenhouse gas emissions by 2047. The electricity sector is responsible for nearly a quarter of US greenhouse gas pollution, according to the EPA.
"It's a disaster for our country," Trump said. "Instead of shutting down power plants, we will open dozens and dozens more, and they'll happen fast."
Meanwhile Biden, forced to abandon his re-election bid, will urge fellow Democrats at their convention on Monday to unite behind Harris in the fight for the White House.
While Democrats gathered at United Centre, home to Chicago's basketball and hockey teams, hundreds of protesters assembled at a nearby park to pressure the party to drop military support for Israel's offensive in the Gaza Strip.
Protesters are assembling as the Democratic National Convention prepares to back Kamala Harris. (EPA PHOTO)
Biden's appearance at the start of the four-day event will serve as a symbolic passing of the torch to his No. 2 after he quit the race under pressure from top Democrats worried that the 81-year-old incumbent was too old to win or serve another four years.
Due to speak at 12.50pm AEST on Tuesday, Biden is expected to portray Trump as a threat to democracy while touting the achievements of the Biden-Harris administration.
Sources said Harris, 59, was likely to join Biden on stage.
Harris will formally accept the nomination on Thursday night with a speech.
