Outside broadcast staff at RTÉ have rejected a management reorganisation plan at a meeting tonight.
Irish TV coverage of the World Cup could be under threat if the workers decide to stage industrial action.
Trade union representatives at the station voted overwhelmingly today to throw out recommendations that effectively supported an RTÉ management decision to farm out OB services.
A SITPU said the recommendations were rejected by a six-to-one majority.
Industrial action over the issue, which would likely take the form of a work-to-rule, was considered "very likely", he said.
Industrial action planned for last month that could have hit RTÉ coverage of the General Election was called off to allow for an investigation by the Industrial Relations Tribunal.