British Airways (BA) is to lodge a formal objection to the proposed changes to the running hours of the London Underground, claiming the changes will force some staff into cars or taxis, or even prevent the completion of their journeys.
Mayor Ken Livingstone wants to run the Tube an hour later on Friday and Saturday nights, but re-open an hour later on Saturday and Sunday mornings to allow engineering work to be carried out.
The Tube now opens at about 5.30am on Saturdays and 7am on Sundays. The changes would mean that Sunday's first trains would not start arriving in central London until about 8.30am.
More than 70,000 people, mostly shift workers, are employed at Heathrow. And Livingstone has admitted that later running could "inconvenience some people".
It is estimated that about 55,000 people use the Tube during the first hour at weekends.
BA, the biggest single employer to be directly affected by the proposals, is advising staff to write to London Underground, according to the London Evening Standard.
Airport owner, BAA, is also advising its 4,000 employees to write to Tube chiefs.
"The change of hours will have an impact on both passengers and staff," a BAA spokesman told the Evening Standard.