Nottinghamshire Police detectives have begun an investigation following two separate reports of two taxi drivers being threatened with a knife over the weekend.
Officers were first called at around 8pm on Saturday in Nidderdale Close in Wollaton, following a driver reporting he was threatened with a knife to his throat and asked for money.
He refused and nothing was taken, before the offender left the vehicle.
Later that night at around 4.30am (Sunday 3 January) in Airedale Walk in Wollaton a second taxi driver was threatened.
The driver collected two men and a woman to arrive at a house in Wollaton, but as they arrived closer to their destination, they got out the car without paying, before the driver was threatened with a knife.
Detective Sergeant Chris Berryman of Nottinghamshire Police is leading the investigation.
He said: "It is totally unacceptable for people doing their job to be threatened in this way.
"We are now appealing for witnesses to help us bring the offenders to justice.
"We believe the two incidents are potentially linked and we are asking for anyone who may have seen anything suspicious to come forward.
"Thankfully no property was stolen and neither driver suffered any injuries.
"It was reported in the second incident that one of the group produced a large knife to warn the driver not to try and follow them.
"If you can help with our enquiries please call 101, quoting incident 79 of 3 January 2021."