Workers on Greater Anglia are to stage a fresh strike in the long-running dispute over the role of train guards, on the day of the 2,000 Guineas horse race at Newmarket.
Members of the Rail, Maritime and Transport union (RMT) will walk out on May 5, followed by a period of refusing to work extra Sundays beyond their agreed rosters.
RMT leaders said they had received the company's "best and final" proposals, which the union described as "unacceptable".
RMT general secretary Mick Cash said: "The vital safety role of guards is still under threat and the extension of driver only operation remains a serious risk."
In a message to members, Mr Cash said: "Greater Anglia remains adamant that the role of the guard will have no involvement in the releasing or closing of train doors.
"The proposal stipulates that 'train drivers will operate the train doors and undertake train dispatch in normal circumstances'.
"Your union reps are of the view that the company cannot be trusted to preserve a safety critically trained employee, let alone a guard on every train."
The union is embroiled in similar disputes with South Western Railway, Southern, Merseyrail and Arriva Rail North.
A protest will be held in Westminster on April 25 to mark the second anniversary of the start of the dispute on Southern.