Train conductors at a rail company are to be balloted for strike action over claims that industrial relations have broken down, it has been announced.
The Rail Maritime and Transport Union (RMT) said it is as a result of plans by East Midlands Trains to use managers to guard their trains on Sundays.
The dispute also centres on a row over conditions. More than 130 conductors will be balloted.
The union said it is urging its members to vote in favour of strike action.
General secretary of the RMT, Bob Crow, said: "The company is acting outside the agreed negotiating machinery and has already poured petrol on the flames by stopping RMT reps being released to undertake normal union duties.
"We want a negotiated settlement to this dispute, but that will not happen while the company is throwing its weight about."
Tim Shoveller, managing director of East Midlands Trains, said: "From the beginning of our franchise we have actually run over 97% of all Sunday services.
"Under the previous franchise, on some Sundays, there were as few as 50% of services running because of a shortage of staff.
"We're confused and disappointed that the RMT do not understand that as a train operator we must be confident that we have enough senior conductors available to operate our trains every day of the week."
East Midlands Trains took over the franchise last November.