http://www.rmt.org.uk/news/rmt-confirms-piccadilly-line-strike-dates090316/

---quote---
RMT confirms strike dates after overwhelming vote on Piccadilly Line
over comprehensive breakdown in industrial relations.
[...]
The ballot for action was called after a prolonged period of industrial
problems on the line – some of which have been directly related to
serious underlying issues with the aging Piccadilly Line fleet. Those
issues have left drivers in a vulnerable position and have been used by
management as a tool to harass and threaten members through misuse of
the disciplinary procedure. There has also been an appalling lack of
consistency by local management when it comes to addressing the
long-running issues impacting on the Piccadilly Line and which RMT, as
the main driver’s union, has raised repeatedly over a number of years.
[...]
---/quote---