A threatening mail containing a white powdered substance was sent to Donald Trump’s son Eric's posh Manhattan residence late Thursday, a source told CBS News. The Secret Service, FBI and New York Police Department are currently investigating the incident.

The mail was reportedly opened by Eric’s wife, who found a white substance inside the package, prompting police, fire crews and the FBI to respond. The envelope was sent for testing, and preliminary test reports revealed that the white substance was non-hazardous, sources told media outlets.

A source told CBS News that the letter, which had a Massachusetts postmark, threatened to harm Donald Trump’s children if he did not withdraw from the race for the Republican presidential nomination.

The letter comes less than a week after an outbreak of violence at Donald Trump’s rallies demonstrating against the candidate’s perceived racism. The 69-year-old also angered immigrants, Muslims and others with his raging speeches during his rallies. Amid the growing controversies surrounding Donald Trump, Republican leaders have pleaded with him to tone down his rhetoric.