The union say that more strikes are planned for this Saturday and next Monday and are set to disrupt services between London and Lincoln.
They will also announce further strike dates in July and August.
Andrew Botham, Aslef Union say they're unhappy at plans by East Midlands Trains to cut the amount of money it, and staff, pay into their pension scheme.
The company says it'll save employees around £500 pound a year in contributions.
Unions argue it's being done to boost profits for East Midlands Trains parent company Stagecoach.