U.S. Secret Service took a Chicago cocktail lounge employee into custody after she spat on Eric Trump.

President Donald Trump's son was at the upscale Aviary bar in the West Loop, which is known for its creative cocktails, when the incident happened Tuesday night.

A person with knowledge of the situation told DailyMail.com a women spat on the president's son immediately after he walked into the upscale cocktail lounge on Chicago's West Side.

She said something to Trump, although it was not immediately clear what it was.

Chicago police quickly made an arrest, and the woman was held in handcuffs for up to two hours. Trump then asked the Chicago Police Department to let her free when told she would otherwise be charged.

A Chicago cocktail lounge employee has been taken into custody by Secret Service after she spat on Eric Trump. Eric (right) is pictured with his brother Donald Trump Jr earlier this month.

'It was purely a disgusting act by somebody who clearly has emotional problems,' Eric told Breitbart News.

'For a party that preaches tolerance, this once again demonstrates they have very little civility. When somebody is sick enough to resort to spitting on someone, it just emphasizes a sickness and desperation and the fact that we're winning.'

'The Secret Service has no comment on this matter,' agency spokeswoman Julia McMurray told DailyMail.com when asked about the incident.

President Donald Trump's son was leaving the upscale Aviary bar (pictured) when the incident happened Tuesday night

Police presence outside Aviary after alleged incident between an employee and Eric Trump around 8:30pm pic.twitter.com/1oIiVfsiKj — Mary Ann Ahern (@MaryAnnAhernNBC) June 26, 2019

The conservative website reported that the female employee approached Eric as he entered the bar in a group.

She muttered something that sounded like it was anti-Trump before spitting at the president's son.

Secret Service agents then took her into custody in handcuffs, but Eric decided not to press charges and she was released.

Anthony Guglielmi, Chief Communications Officer, tweeted: 'CPD was on scene and assisting the United States Secret Service with a law enforcement matter. Any and all inquiries regarding a federal protectee must be directed to the Secret Service.'

An NBC5 Chicago reporter tweeted a photo showing police at the scene at around 8.30 p.m.

He also shared photos of the Chicago skyline on Tuesday evening showing Trump Chicago (seen above)

The Aviary is an upscale cocktail lounge on Chicago's West Side.

Eric posted on Instagram shortly after the incident, sharing a Socrates quote: 'When the debate is lost, slander becomes the tool of the losers.'

He also shared photos on social media of the Chicago skyline on Tuesday evening showing Trump Chicago.

He tweeted: 'Always love visiting @TrumpChicago! It is one of the most beautiful buildings in the world! @TrumpHotels.'

Eric travels with Secret Service protection as the president's son, including on a recent trip to the United Kingdom this month with wife Lara, Ivanka Trump, Jared Kushner, Donald Trump Jr. and Tiffany.

Eric Trump and Donald Trump Jr. are the two principal executives who run the Trump Organization, the president's family real estate business.

Donald Trump Jr. has also been a regular at campaign rallies.

Eric took to Instagram shortly after the incident sharing a Socrates quote

The Aviary is seen above. It is located in the West Loop and features creative cocktails

JUST A SPLASH: The cocktail bar where Eric Trump was spit on features a variety of high-end beverages

The cocktail lounge features sleek images of back-lit drinks on its web site

Eric was the recipient of a death threat during the 2016 campaign. Daniel Frisiello of Beverly Hills last year pleaded guilty to leveling threats and carrying out hoaxes. Among them was a letter to Eric Trump that said: 'If your father does not drop out of the race, the next letter will not be fake.'

The threat resulted in a hazmat response to his New York apartment.

He told Fox News last year: 'I've been threatened. Our family's been threatened. All of us. We've all had white powder show up at our house.'

The incident at the bar does not appear to have posed any physical threat to the president's son, but it recalls some tense confrontations that White House staffers experienced while out in public last year.

A woman was charged with assaulting White House counselor Kellyanne Conway at a Mexican restaurant in Bethesda in 2018.

'I turned around, and the woman had grabbed my hands,' Conway told CNN in February. 'She was just unhinged. She was out of control. I don't even know how to explain her to you. She was just — her whole face was terror and anger.'

Outgoing White House press secretary Sarah Sanders was kicked out of a restaurant in Virginia.

'I always do my best to treat people, including those I disagree with, respectfully and will continue to do so,' she tweeted after getting kicked out for working for Trump.