RMT union members working on Heathrow Express are set for more industrial action over the bank holiday weekend.
Workers plan to walk out for 24 hours from 3am on Friday of this week and for a further 24 hours from 3am on Monday of next week.
Action short of a strike is set to take place between the two strikes.
Almost half the workforce is threatened with redundancy. The remaining workers face a ten-year pay freeze.
Bosses want train drivers to take on the role of evacuating passengers in an emergency so they can get rid of other onboard workers.
The union said the cuts “amount to an all-out assault on pay, jobs and safety”.
Bosses have now withdrawn their pay offer altogether.