Drivers on parts of London Underground are to strike on the day of President Donald Trump's visit to the capital next month, in a row over working conditions and staffing.
Members of the Rail, Maritime and Transport union on the Piccadilly Line will walk out from 9pm on July 11 until midnight on July 14.
The US president is visiting the UK on July 13.
Around half a million passengers a day travel on the Piccadilly Line, which links central London to Heathrow Airport.
The RMT accused London Underground of failing to employ enough drivers, continued problems with the "ageing" Piccadilly Line fleet and the alleged breaking of agreements.
RMT general secretary Mick Cash said: "There have been repeated problems on the Piccadilly Line going back a number of years which have led to dispute after dispute and the failure of LU management to get a grip has tipped the situation over the edge yet again.
"That is why we have had no option but to put on these strike dates.
"Every effort by RMT reps to negotiate a settlement has been obstructed by the company and it is now down to London Underground bosses to start listening to their members, take the raft of issues at the heart of this dispute seriously and start engaging in a way that will allow us to make some genuine progress."