President Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE’s daughter-in-law was taken to the hospital as a precaution on Monday after she opened a letter containing an unidentified substance, the New York City Police Department said.

The letter was addressed to Vanessa Trump’s husband, Donald Trump Jr. Don John Trump'Tiger King' star Joe Exotic requests pardon from Trump: 'Be my hero please' Zaid Jilani discusses Trump's move to cancel racial sensitivity training at federal agencies Trump International Hotel in Vancouver closes permanently MORE He is the eldest son of the president and his first wife, Ivana.

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An initial review indicated the the substance was not hazardous, police said.

The Secret Service confirmed in a statement that it is working with law enforcement partners to investigate a suspicious package sent to one of its protectees.

The Secret Service and our law enforcement partners in New York City are investigating a suspicious package addressed to one of our protectees received today in New York, New York. This is an active investigation and we cannot comment any further. — U.S. Secret Service (@SecretService) February 12, 2018

NBC News first reported the incident. Three residents in total were taken to the hospital after the letter was opened, according to NBC.

Trump Jr. is leading the Trump Organization with his younger brother, Eric. He has been a central figure in the investigation into Russian meddling in the 2016 presidential election after he met with a Russian lawyer who promised damaging information on Democratic nominee Hillary Clinton Hillary Diane Rodham ClintonWhat Senate Republicans have said about election-year Supreme Court vacancies Bipartisan praise pours in after Ginsburg's death Trump carries on with rally, unaware of Ginsburg's death MORE.

Updated: 3:03 p.m.