Donald Trump Jr. reported Monday his wife, Vanessa Trump, and children are safe after Vanessa Trump opened a letter containing an unidentified white powdery substance, an incident he called “truly disgusting.”

“Thankful that Vanessa & my children are safe and unharmed after the incredibly scary situation that occurred this morning. Truly disgusting that certain individuals choose to express their opposing views with such disturbing behavior,” Trump Jr. tweeted Monday.

The letter was addressed to Donald Trump Jr. at the midtown Manhattan apartment belonging to Vanessa Trump’s mother.

After opening the suspicious letter, Vanessa Trump called 911. She said she began coughing and felt sick.

Vanessa Trump and two others were taken to New York Presbyterian-Weill Cornell Medical Center for evaluation.

The New York City Police Department said the substance was not toxic.

The U.S. Secret Service is investigating the incident.

White House press secretary Sarah Sanders told reporters that President Trump spoke with his daughter-in-law earlier Monday.