Rail workers on the Heathrow Express service will walk out for 48 hours next Tuesday, April 29.
Management said it hoped to resolve the dispute ahead of the planned strike, but said it had a "robust" contingency plan in place that would allow it to run regular trains during any industrial action.
The strike is over plans to reorganise the workforce, which management says will save £6 million over five years but the Rail, Maritime and Transport Union claims it could threaten more than 200 jobs.
Members of the union plan to walk out on 03:00 hours on April 29,
The strike is due to be held just eight hours after London Underground workers are due to start five days of strike action over ticket office closures.
RMT members at London Underground will walk out from 21:00 hours on April 28 for two days and again on May 5 for three days.
