New York City Mayor Bill de Blasio faced a crowd of angry protesters Monday at a raucous rally promoting the city’s Green New Deal inside the lobby of Trump Tower, where the Democrat threatened President Trump’s family company with millions of dollars in fines if his buildings don’t comply with new environmental standards.

Speaking in front of the same escalators where Trump launched his 2016 campaign, de Blasio blasted the president's rollback of Obama-era environmental policies, his move to pull the United States out of the Paris Climate Agreement and his appointment of climate change skeptics to the Cabinet.

“His buildings are one of the biggest polluters in New York City,” de Blasio said. “Cut your emissions or we’ll cut something you really care about.”

De Blasio, who is mulling a Democratic presidential run, added: “We’ll take your money.”

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The mayor, though, was forced to shout for much of his speech amid jeers from a crowd of about a dozen protesters inside the lobby of Trump Tower, which also had music blasting over the speakers. A number of protesters rode up and down the escalator behind de Blasio carrying cardboard signs with slogans like “Worst Mayor Ever,” “Failed Mayor,” and “Trump 2020.”

De Blasio said he did not mind the protesters and added that it was “so nice for them to serenade us.”

“They’re scared of the truth,” he said. “Anyone that has a problem with saving the planet, I have a problem with them.”

The rally for the city’s Green New Deal was originally scheduled to be held in front of Trump Tower, but was moved into the lobby due to inclement weather.

New York City’s own Green New Deal plan – officially called The Climate Mobilization Act and modeled after the one proposed in Congress by Rep. Alexandria Ocasio-Cortez, D-N.Y. – passed the City Council last month in a 45-2 vote. De Blasio has not yet signed the legislation but is expected to soon.

The deal is actually a package of 10 bills meant to curb carbon emissions in the country’s largest city by carrying out measures that will be “the equivalent of taking more than one million cars off the road by 2030,” according to New York City’s Committee for Environmental Protection Chair Costa Constantinides.

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But the main facet of the deal is the plan clamp down on emissions from the city’s famed skyscrapers with a goal of reducing overall emissions by 40 percent by 2030. Buildings create almost 70 percent of the city’s greenhouse gas emissions, according to a recent survey.

“The first of any major city on the Earth to say to building owners, ‘you've got to clean up your act, you've got to retrofit, you've got to save energy,’” de Blasio said last month. “If you don’t do it by 2030 there will be serious fines, as high as $1 million or more for the biggest buildings.”

Upgrades to buildings in order to meet the new standards are expected to cost owners around $4 billion – a figure that has the city’s powerful real estate lobby up in arms.

“The bill that passed…will fall short of achieving the 40 x 30 reduction by only including half of the city’s building stock,” Real Estate Board of New York President John H. Banks said in a statement. “The approach taken today will have a negative impact on our ability to attract and retain a broad range of industries, including technology, media, finance, and life sciences, that provide opportunity and continued economic growth that is so important for our city.”

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New York is not the only major American city to push its own version of the Green New Deal.

Los Angeles Mayor Eric Garcetti released a plan last month to make the city carbon neutral by 2050.

“Politicians in Washington don’t have to look across the aisle in Congress to know what a Green New Deal is — they can look across the country, to Los Angeles,” Garcetti said. “With flames on our hillsides and floods in our streets, cities cannot wait another moment to confront the climate crisis with everything we’ve got. L.A. is leading the charge, with a clear vision for protecting the environment and making our economy work for everyone.”

Fox News’ Tamara Gitt contributed to this report.