A Michigan police officer has been placed on administrative leave after a black couple who toured his home found a Ku Klux Klan application framed in his bedroom.

Rob Mathis posted a picture of the document on Facebook and said he stopped the tour and declined to make an offer on the house.

On Thursday, the City of Muskegon said in a statement that the police department had launched an internal investigation into the incident.

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A black couple looking to buy a home toured a Michigan police officer's house, only to find it covered with Confederate flags and even a framed application for the Ku Klux Klan.

Rob Mathis posted about the incident on Facebook, saying he immediately stopped the tour and told the realtor he wouldn't make an offer.

"I feel sick to my stomach knowing that I walk [sic] into the home of one of the most racist people in Muskegon hiding behind his uniform and possibly harassing people of color and different nationalities," Mathis said.

He continued: "To the officer, I know who you are and I will be looking at resources to expose your prejudice. As for now pictures speak 1000 words."

Mathis attached a photo of the aged, yellowed application, which was framed and hanging on the bedroom wall. The top of the document reads, "Application for Citizenship in the Invincible Empire, Knights of the Ku Klux Klan."

Read more: An interracial couple's house mysteriously exploded in Ohio. Investigators found a swastika and racist slur painted in the garage.

On Thursday, the City of Muskegon said in a statement that the police department had launched an internal investigation into the incident, and placed the officer on administrative leave.

Mathis, a US Army veteran, told MLive he felt an obligation to speak up about the KKK application because it belonged to a public servant.

"I just felt so gross after being in that house, like I needed to be dipped in hand sanitizer," Mathis said. "He can't be impartial and fair to minorities if that's how he thinks. I was just mortified."