Police in New York said Monday that a letter containing “an unidentified substance” was mailed to the home of Donald Trump Jr., the president’s oldest son.

Trump’s wife, Vanessa, opened the letter and was taken to a hospital as a result, according to the New York Police Department.

She was “not feeling well” after opening the letter, police said. The Associated Press reported that she was coughing and feeling nauseated.

A preliminary assessment showed that the substance is not suspicious, said Lt. John Grimpel, a New York police spokesman.

In a Twitter message posted late Monday afternoon, Trump Jr. said that his wife and children were “safe and unharmed.” He also suggested that the letter may have been motivated by political rancor, writing that it was “disgusting that certain individuals choose to express their opposing views with such disturbing behavior.”

The Secret Service, which is tasked with protecting the immediate families of presidents, confirmed only that it was investigating a suspicious item sent to someone it is protecting. The agency did not specifically mention Trump Jr. or his family.

“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,” the agency said in a statement. “This is an active investigation and we cannot comment any further.”

Trump Jr., along with his brother, Eric, took over managing the Trump Organization after their father won the presidency. The company did not respond to a request for comment Monday.

This story, first posted at 1:59 p.m., has been updated.