PHILADELPHIA -- The U.S. Mint in Philadelphia put an employee on administrative leave after a noose was found at the plant on the chair of an African-American colleague.

The unidentified employee created the noose with rope used to seal coin bags once they're full, according to the president of the mint workers union.

Surveillance video captured the employee's actions. Around 3 p.m. June 28, the white male coin maker walked across the factory floor with the noose in hand.

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Many African-American workers called and texted the union president the next day, and the U.S. Treasury Department's inspector general launched an internal investigation.

CBS Philadelphia reports mint officials declined to talk about the incident, but sent an email statement that reads in part: "We have absolutely zero tolerance for the kind of misconduct reported at the Mint. Secretary Mnuchin has directed that this matter be handled swiftly and seriously. The investigation is moving ahead quickly. We strive every day for a workplace environment that is welcoming and safe for all."

Loops of rope have long been used to intimidate African-Americans because they evoke lynchings. The nonprofit Equal Justice Initiative said there were 4,075 lynchings of blacks in the South to spread racial terror between 1877 and 1950.

For blacks, the noose is "comparable in the emotions that it evokes to that of the swastika for Jews," the Anti-Defamation League said