Business groups in the capital have condemned planned walkouts by staff on the London Underground (LU) network.
On Thursday morning, a 24-hour strike remained in place to hit the Piccadilly Line on Christmas Eve - one of the biggest shopping days of the year.
Walkouts were called after a tube driver was demoted by the LU for failing to stop at red signals. Separately, 330 signal workers are in a dispute the LU over pay, hours and possibly job cuts.
Jo Valentine, chief executive of London First, said: "Striking on Christmas Eve seriously jeopardises the important Christmas retail sales.
"The Piccadilly line includes Knightsbridge, Covent Garden and Piccadilly Circus stations to name but a few. Retailers and Londoners have done nothing to deserve this treatment.
Dan Bridgett of the London Chamber of Commerce added: "The unions are sticking two fingers up at businesses and their customers.
"Much of the retail sector in the capital is reporting disappointing sales in the pre-Christmas period. To take a major arterial route into London out of action on one of the busiest days of the year is the last thing that either shopkeepers or shoppers want."
At time of writing, last-ditch talks were due to start - although hopes of a settlement were hampered by accusations of stalling from both sides of the dispute.
