The GMB union says it expects between five and ten thousand people to join a march through west London today in protest against the closure of emergency departments at several hospitals.
Plans have been outlined for the closure of facilities at Charing Cross and Hammersmith & Fulham Hospitals, and Ealing and Central Middlesex Hospitals.
The Union says the closures would lead to longer waiting times at other hospitals.
A spokesperson for NHS North west London said the plan was currently being consulted upon, and they would like to hear people's views.
The march will start in Shepherd's Bush at midday.
More top news
A protest is planned 6pm today outside Stoke Newington police station
Travellers left behind an estimated 250 tonnes in Bromley
Several South West Trains services have been cancelled or delayed by up to 90 minutes