New York City Mayor Bill de Blasio Bill de BlasioOVERNIGHT ENERGY: California seeks to sell only electric cars by 2035 | EPA threatens to close New York City office after Trump threats to 'anarchist' cities | House energy package sparks criticism from left and right EPA threatens to close New York City office after Trump threats to 'anarchist' cities New Year's Eve in Times Square to be largely virtual amid pandemic MORE (D) was heckled Monday during a press conference in the lower part of Trump Tower, where the mayor was introducing new regulations curbing energy use by buildings in the city.

The New York Times reported de Blasio's news conference was marred by supporters of President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE holding signs mocking the mayor and promoting Trump's 2020 reelection campaign as they rode up and down the escalators of the lobby of Trump Tower in the background of de Blasio's speech.

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Building staff also blasted famous hits from Tony Bennett during the event, according to the Times, while Trump supporters booed and whistled at the mayor.

De Blasio is considering a bid for the presidency in 2020 and is set to announce this week whether he will join a crowded field of more than 20 Democrats vying for the party's nomination to take on Trump.

The New York City mayor threatened the Trump Organization and other businesses in the city with fines at Monday's press conference if they do not reduce their carbon emissions by 2030, a provision of his newly passed citywide law.

“It doesn’t matter who you are, even the president of the United States, you have to obey the laws of New York City,” he said Monday.

On Twitter, the mayor responded to the Trump Organization's antics, calling the scene a "temper tantrum."

".@realDonaldTrump is running scared from NYC’s Green New Deal. The temper tantrum his organization threw at Trump Tower today is proof," de Blasio wrote.

"You're on notice, Donald: we won't let you mortgage our future for your real estate. Fix your buildings or pay the price," he tweeted.