Heathrow Express services were expected to suffer further disruption today after a strike among drivers and other staff in two separate disciplinary disputes.
The strike yesterday was said to be "solidly'' supported.
Members of the Rail Maritime and Transport union walked out for 24 hours just after mid-day yesterday, forcing the company to operate an amended service between the airport and central London.
The union said the strike had had a "serious impact'' on services which would continue into today's rush hour.
General secretary Bob Crow said yesterday: "Our members are rock solid in their support for the strike and their colleagues and the management should get the message and start talking.''
Heathrow Express said it was disappointed with the industrial action and apologised to passengers for any inconvenience to their journeys.
Fewer services were expected to run until this afternoon, a few hours after the strike ends.
A second 24-hour stoppage is due to start from the same time on March 11, while union members will not work any extra hours over the weekend of March 3-4.
The action is in support of a sacked driver and the suspension of an RMT local official and follows ballots in support of strikes.
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