A bus driver had to stop the vehicle twice while travelling between Kettering and Corby after three passengers became abusive to him.
The driver and a colleague, travelling as a passenger, were subjected to abuse after two men who appeared to be drunk got on the bus in Newland Street, Kettering, and were joined by a third man.
A police spokesman said: “During the journey, the three men were abusive to the bus driver and his colleague.
“The driver stopped the bus twice before coming to a final stop in Oakley Road, Corby, near to the bus stop outside Lidl.”
Police are appealing for witnesses to the incident which took place between 9.10pm and 9.30pm on Thursday, August 1, and officers would particularly like to speak to two women who got off the bus when the incident happened.
One of the offenders is white, of skinny build, 50 to 55-years-old and about 5ft 9in. He had no front upper teeth and was unshaven. He wore a dark blue top and light coloured tracksuit bottoms.
The second man is white, about 50-years-old, about 5ft 9in, with black, combed-back hair. He wore a black top and light blue jeans, and was carrying a large Sports Direct bag.
The third man is described as being of mixed race.
Witnesses to this incident, or anyone with information about it, can call Northamptonshire Police on 101 or information can be given anonymously to Crimestoppers on 0800 555111.