The RMT union said that it was holding a strike ballot "in response to London Underground riding roughshod over agreements and abusing a range of agreed policies and procedures".
They are unhappy with plans to split a depot in Acton Town into two - claiming that that tube bosses are "ripping up rosters and booking times" and "refusing perfectly reasonable requests for decent staff facilities".
RMT General Secretary Bob Crow said:
"Driver and instructor members on the Piccadilly Line are furious at this unilateral attack by the company on working conditions, agreements and procedures and we are moving forwards with plans for a ballot for strike action.
"We will of course be in talks with our sister drivers union ASLEF and London Underground should be in no doubt about the unions determination to protect working conditions and to stop the abuse of procedures."
More top news
Tube bosses have made a new offer to drivers - to try to break the deadlock over the launch of the new Night Tube service
In an interview with ITV News, the Mayor said his 'sympathies were with the PKK' - a proscribed Kurdish terror group
Martin Stew has the forecast: