Nearly 400 tube drivers across the Piccadilly Line are set to go on strike after accusing bosses of a campaign of 'bullying, harassment and intimidation'.
The Rail Maritime and Transport (RMT) union confirmed three separate strike dates, after 85% of those voting in the ballot supported industrial action.
Union members have planned three 24-hour walk-outs from the evening of Wednesday 23 March and again from midday on Tuesday 19 April and midday on Thursday 21 April for 24 hours.
Around 600,000 passengers a day travel on the Piccadilly line on average. It also provides the only Tube service to Heathrow airport.
In a statement the union said issues had arisen during a 'prolonged period of industrial problems on the line,' some of which directly relate to 'serious underlying issues with the aging Piccadilly Line fleet'.
It criticised Underground bosses for not addressing long-standing issues and using them as a management tool 'to harass and threaten members through misuse of the disciplinary procedure'.
RMT general secretary Mick Cash said: 'The wholesale abuse of procedures and agreements by management on the Piccadilly Line is rife and amounts to the development of a campaign of bullying, harassment and intimidation that the union will not allow to continue.
'The combined weight of these abuses and failures has built up to a comprehensive and fundamental collapse in industrial relations that the company have done nothing to address and which has now left RMT with no option but to call strike action following the overwhelming vote of by our members.The union remains available for talks.'
Transport for London urged the union to continue discussions, with operations director Pat Hansberry telling the BBC: 'It is disappointing that the RMT is once again threatening unnecessary strike action without seeking to resolve these local issues with us first.'
