Official engagement photograph of Prince William and Catherine Middleton. Copyright 2010 Mario Testino.
London subway drivers are threatening to strike on the day of Prince William and Kate Middleton's wedding.
The ASLEF union said Monday its members might walk out April 29 in a dispute over holiday pay.
Middleton and the prince are due to marry in Westminster Abbey. The day is a public holiday, so a strike would not hit commuters, but it could disrupt thousands of people traveling to central London for the event.
The pay dispute already has seen drivers strike on the Dec. 26, the Boxing Day holiday.
Last month, union leaders predicted that walkouts could become widespread in 2011 as workers feel the impact of Britain's austerity measures -- and could affect the royal wedding.