President Trump got right to work in the Oval Office on Monday, promising to “massively” cut regulations and taxes during meetings with captains of industry and union leaders.

He started off a whirlwind day at a breakfast with business leaders at the White House, where he pledged to cut regulations by 75 percent or “maybe more.”

“We are going to be cutting taxes massively for both the middle class and for companies. And that’s massively. We’re trying to get it down to anywhere from 15 to 20 percent,” Trump told the dozen execs at the Roosevelt Room Monday, the day he considered his official start day.

He told the business titans — including Mark Fields of Ford, Elon Musk of SpaceX and Michael Dell of Dell Technologies — that he was focusing on trade and the economy as part of his vow to “make America great again.”

“It’s what the people wanted. It’s one of the reasons I’m sitting here instead of someone else sitting here. I think it’s something I’m good at,” Trump said.

The president said that regulations are choking businesses and that he intends to fast-track job plans to build factories and cut the corporate tax rate from 35 percent to around 15 percent.

“A bigger thing, and that surprised me, is the fact that we are going to be cutting regulation massively. Now we are going to have regulation, and it will be just as strong and just as good and just as protective of the people as the regulation we have right now,” the president said.

While he talked up bringing jobs back to America, he warned the tycoons that companies shipping jobs abroad would feel his wrath.

“If that happens, we are going to be imposing a very major border tax on the products when it comes in,” he said.

Calling the execs “great people,” Trump said he would like to meet with them four times a year to stay attuned to the business community.

Later, Trump talked jobs and trade with labor leaders.

“We are going to stop the ridiculous trade deals that are taking everybody out of our country and taking companies out of our country, and it’s going to be reversed. It’s inconceivable to me that this was allowed to happen in the first place,” he told the union officials.

“And I’m not blaming President Obama for this. I’m blaming many, many years long beyond Obama. Believe me. This has been going on for decades. And it is a trend that we are going to stop cold.”

The union heads included Sean McGarvey of North America’s Building Trades Unions; Terry O’Sullivan of the Laborers’ International Union of North America; Joseph Sellers of the International Association of Sheet Metal Air, Rail and Transportation Workers (SMART); Doug McCarron of the United Brotherhood of Carpenters; and Mark McManus of the United Association of plumbers, fitters welders and service techs.

Nearly all major unions endorsed Hillary Clinton during the presidential campaign.