Police officers want to trace two men after a member of staff was threatened on a train travelling between Meadowhall and Rotherham.
British Transport Police said two men boarded a train at Rotherham and refused to show an inspector their tickets.
They became aggressive when they were asked to leave and threatened the member of staff concerned during the incident on Tuesday, August 25.
PC Fiona Poyner said: “Two men boarded the train at Rotherham at 4.45pm.
“A member of onboard staff asked to see their tickets, but they refused to comply.
“One of the men became verbally aggressive, threatening the member of staff.
“The men were asked to leave, but refused.”
Officers investigating the incident have examined CCTV footage in a bid to find the culprits.
PC Poyner added: “Those who work on the rail network have the right to do so without the fear of violence.
“The men involved in this incident left their victim in no doubt of their intentions.
“We need to find them. I think the people in the image we are issuing today have information which could assist us. Who are they?”
Call 0800 40 50 40 quoting reference PSUB/B9 of September 22.