By Shimon Prokupecz

NEW YORK, N.Y., (CNN) — A threatening letter addressed to Donald Trump’s son Eric Trump contained a suspicious powder in its envelope, a law enforcement source said Friday.

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The substance, which was delivered to a New York City Trump building, was tested and appears to be lemonade mix, according to initial reports.

Eric Trump’s wife was going through the mail when she picked up the envelope and powder came out, the source said.

There was a handwritten note in the envelope making threats if Trump’s father, the Republican front-runner, does not drop out of the race.

The Secret Service is investigating along with FBI, according to the source.

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It was postmarked March 7 from a post office in Boston, the source said, and Trump alerted authorities about the letter Thursday, J. Peter Donald, director of communications at the New York Police Department, said Thursday.

No injuries have been reported in connection with this incident, Donald said Thursday.

In recent weeks, there have been similar incidents at offices for the campaigns of Sens. Ted Cruz and Marco Rubio.

(The-CNN-Wire ™ & © 2016 Cable News Network, Inc., a Time Warner Company. All rights reserved.)

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