A video of a white police officer quizzing a black driver is being investigated by the police watchdog.
The footage, shot in Ely, Cambridgeshire, in 2015, was shared on Facebook in June as Black Lives Matter protests took place.
A complaint was first made to Cambridgeshire Police last month.
It was then referred to the Independent Office for Police Conduct (IOPC) which is investigating the "complaint of racial profiling".
Footage posted on social media by the driver's sister purports to show an unidentified officer telling 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.
Sal Naseem from the IOPC said: "Although this incident is from five years ago it has raised concerns about public confidence in policing."
He said the investigation would look at whether the officer's actions were "appropriate and proportionate and if racial discrimination played a part in the incident".