About 150 senior conductors will be asked whether to strike or take other industrial action, following a row over Sunday shift cover.

If a strike goes ahead, it would hit local services from Nottingham but would not affect trains to London.

The row started when East Midlands Trains told the Rail, Maritime and Transport (RMT) Union it was planning to ask managers to provide emergency cover on senior conductor shifts on Sundays.

A number of Sunday services had to be cancelled because of a lack of senior conductors - who are responsible for the safety of the train and passengers.

East Midlands Trains, which took over the franchise from Central Trains in November last year, has a voluntary arrangement for covering Sundays.

And with no cash incentive, many senior conductors were choosing not to work.

A spokesman for the RMT said: "East Midlands Trains say they have had problems covering Sundays, which has led to the cancellation of some services.

"They proposed to use managers and all sorts to cover the job. That is unsafe in our view. A senior conductor is in charge of a train - not the driver.

"They are responsible for the safety of the train and customers. There is strict training for them.

"If there is a problem with Sunday coverage it is because they are not paying enough."

The spokesman said the company had introduced an ad-hoc payment system for senior conductors which had helped ensure the Sunday posts were covered in the past two weeks. But he said when RMT officials asked for this arrangement to be made formal, the company made the proposal for emergency cover by managers.

"We have said we will sit down and negotiate with the company over it but we are not looking for any dilution of safety," he said.

The ballot is understood to involve a total of 150 senior conductors - including about 110 based in Nottingham.

It could be up to five weeks before any industrial action comes into effect.

East Midlands Trains said it was "very disappointed" about the ballot.

The company said it had already enhanced Sunday payments for senior conductors to encourage volunteers.

Managing director Tim Shoveller said: "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.

"This is a fantastic improvement, achieved through better management and with the flexibility and commitment of our staff.

"I thank our staff for their continued dedication but we must now find a permanent solution to ensure the reliability of Sunday services.

"We're confused and disappointed that the RMT do not understand that we must be confident that we can operate our trains every day of the week for passengers. It's not something we can leave to chance."