Rail staff could go on strike over bonus payments for working during the Olympics.
Greater Anglia station staff and conductors in the Rail, Maritime and Transport union (RMT) are set to vote on whether to take industrial action.
The vote comes after RMT representatives rejected a Greater Anglia offer on Olympic reward payments.
RMT general secretary Bob Crow said: "Greater Anglia have deliberately dragged their feet over this crucial issue knowing the clock is ticking down."
Although the union refused to speculate on possible dates of action in the event of a yes vote, a strike could take place during the Olympics.
A Greater Anglia spokesman said: "We're disappointed that the RMT union is intending to organise a ballot.
“We will continue to progress the constructive discussions that are taking place over this matter with the RMT and our staff representatives."
Read more in next week's Times.