Passengers travelling to Heathrow are likely to see journeys disrupted as staff prepare to walk out as part of an industrial dispute.
Members of the Rail Maritime and Transport union are preparing for two 24-hour strikes on February 26th and March 11th.
The strikes are in relation to two separate disciplinary disputes.
Up to 250 workers involved in the disputes will also refuse to work any additional hours for 48 hours from 03:00 on March 3rd.
The action is in support of a sacked driver and in protest against the suspension of a union activist.
In a statement RMT general secretary Bob Crow said: “Instead of using the period between the ballot result and the announcement of industrial action to negotiate a settlement, Heathrow Express have instead opted to ratchet up their attacks in an act of blatant provocation.”