Trump Tower stands along 5th Avenue in Manhattan as police stand guard outside following an earlier protest against Republican presidential candidate Donald Trump in front of the building on March 12, 2016 in New York City.

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Trump struck a deal with New York City in 1979 for a major expansion of the now-famous building

But the agreement stipulated that the atrium of the building be kept open to the public for certain times every day

CNN  — 

The New York City Department of Buildings confirmed Wednesday that it is investigating the use of the Trump Tower atrium for campaign events, which may violate an agreement Donald Trump made to keep parts the building open to the public when he built the landmark.

Department spokesman Joe Soldevere told CNN that the “Department of Building’s enforcement unit is investigating whether the atrium was improperly closed to the public.”

Soldevere said the probe was sparked by Tuesday’s press conference at Trump Tower. Reuters first reported the investigation by the Department of Buildings.

A message left with the Trump campaign was not immediately returned on Wednesday.

Trump struck a deal with New York City in 1979 that allowed for extended zoning of the now-famous building on Fifth Avenue in Manhattan. But the special permit stipulated that the atrium of the building “be accessible and kept open to the public from 8:00 a.m. to 10:00 p.m. daily.”

While the deal said the atrium could be closed to the public up to four times a year with permission, Soldevere told CNN that they had “received no such requests” from the Trump campaign. An official with the city planning department added that no requests had been received in the past two years. And Trump has frequently used the space for campaign events, including interviews, press conferences and even the announcement of his campaign.

New York City Mayor Bill de Blasio has endorsed Hillary Clinton for president. Austin Finan, a spokesman for de Blasio, said, “Despite what he may think, the rules and laws of this city apply to everybody, including Mr. Trump. Mr. Trump should honor his agreement with the city to keep the space open to the public.”

CORRECTION: A previous version of this story incorrectly attributed the news agency that first reported the investigation. Reuters broke the story.

CNN’s David Shortell contributed to this report.