A video showing a white police officer quizzing a black driver has been referred to the police watchdog.
The footage, shot in Ely, Cambridgeshire in 2015, was shared widely on Facebook as Black Lives Matter protests took place.
It indicates the driver was pulled over because he was black.
A formal complaint, received since the footage was published, resulted in a referral to the Independent Office for Police Conduct.
The footage was posted on social media by the driver's sister, in which the unidentified officer tells the driver there are county lines drug problems in the area involving black males.
The police officer says he does "not see many black males" in Ely and pulled the driver over because he had not seen him before.
The driver does not accuse the officer of being racist, but suggests he would not have been stopped if he were white - a point which the officer appears to accept.
Cambridgeshire Police previously said it had not received any formal complaints about the officer's behaviour.
Chief Constable Nick Dean said he could "understand why such a video clip would be concerning, especially with the current events surrounding the death of George Floyd".
The death of Mr Floyd in the United States in police custody last month has sparked global protests.