Supporters of President Donald Trump crashed New York Mayor Bill de Blasio’s press conference touting the city’s “Green New Deal” inside the lobby of Trump Tower on Monday morning, holding signs with insults directed at the far-left Democrat.

Speaking at a podium steps from the spot where President Donald Trump announced his own presidential run in 2015, the Democrat said he had come to Trump Tower to promote a new city air pollution law requiring skyscraper owners to cut greenhouse gas emissions or face fines.

De Blasio said Trump’s buildings in the city could face a combined $2.1 million in annual fines if they don’t reduce emissions by 2030.

“President Trump, you’re on notice. Your polluting buildings are part of the problem,” he claimed.

However, de Blasio’s speech was all-but drowned out by a throng of Trump supporters who demonstrated behind him on the building’s escalators, booing, whistling, chanting and holding up signs with messages including “Failed mayor” and “Worst mayor ever.” Footage of the heckling was shared to social media.

Elevators as prop pic.twitter.com/RDs09qJFtI — Mike Sacks (@MikeSacksEsq) May 13, 2019

Trump supporters try to take over de Blasio’s green new Deal announcement with shouts, whistles and signs pic.twitter.com/4JOqn3yCMU — Julia Marsh (@juliakmarsh) May 13, 2019

.@NYCMayor says Trump Org “a little sensitive,” adds it’ll see how much it has to pay under NYC Green New Deal. Note anti-de Blasio, pro-Trump signs in background pic.twitter.com/VUdcWRB70M — Emily Ngo (@epngo) May 13, 2019

I'm laughing so hard! Snake oil salesman de Blasio tried to sell the ludicrous Green New Deal, while Trump supporters rode the escalator behind him with signs. This is magical. pic.twitter.com/DUVYfPod2E — #ThePersistence (@ScottPresler) May 13, 2019

Loud music also played over the building’s sound system for part of the event. De Blasio had to shout to be heard.

“It’s so nice of them to serenade us at Trump Tower. Clearly, they are uncomfortable with the truth,” he said.

Under a deal that President Trump struck with the city decades ago, Trump Tower’s lobby is considered a public space for much of each day.

New York City’s $14 billion “Green New Deal” aims to reduce emissions by roughly 30 percent. The plan will ban new glass buildings deemed “inefficient” and strive for carbon neutrality by 2050.

The Associated Press contributed to this report.