Drivers and guards for the main rail company in the east of England have voted for strike action.
Rail union RMT said the planned walkout was in response to a dispute with Greater Anglia over the role of guards and driver-only trains.
The union says the company "has failed" to give a guarantee on the future of guard roles on its services and there is a concern for passenger safety.
Greater Anglia said it wanted to resolve issues and avert the action.
The firm is replacing its trains with new ones during 2019/20.
They feature technology which enables drivers to open and close doors, rather than relying on guards.
Greater Anglia said it valued its conductors "highly" and they had guaranteed jobs until the end of its franchise in October 2025.
It said guards would still have a customer service role to play.
RMT said more than 200 Greater Anglia conductors, on a 90% turnout, voted by nine-to-one for strike action.
Three-quarters of drivers took part in the ballot, two to one voting to walk out.
It has not yet been confirmed when the industrial action will take place.
RMT general secretary Mick Cash said: "Greater Anglia have been given every opportunity to give a guarantee on the future role of the guard on their services.
"They have failed to do so and that left us with no alternative but to move to a ballot in the interests of rail safety.
"Our members have now voted by massive majorities for action and it's now down to the company to wake up and take note and to seize the opportunity to give us the very simple assurances on the future of the guards.
"The union remains available for further talks around the crucial issue of the guard guarantee."