Workers for Heathrow Express are planning a 48-hour strike next week, the Rail, Maritime and Transport Union (RMT) has announced.
Members of the union plan to walk out on 03.00 BST on 29 April (Tuesday) amid concerns more than 200 jobs are at risk in a reshuffle.
The rail operator hopes to resolve the dispute in the next few days.
Keith Greenfield, managing director of HEX said: “We remain eager to continue our productive discussions with RMT union reps and we still hope they choose to resolve the dispute around the table rather than through damaging industrial action.
“A strike is not the answer. It will increase costs when we are trying to reduce them, taking us further away from what we need to do to secure our business for the future.
“However, we will not let it stop us providing an excellent service for our customers. We have a robust contingency plan that will enable us to run regular trains for as long as any industrial action lasts.”
RMT members of the London Underground also plan to strike next week, from 21.00 on 28 April for two days and again on 5 May for three days.