The RMT has confirmed strike dates after tube drivers on the Piccadilly line voted to go on strike following a breakdown in industrial relations.
The union said there had been an overwhelming vote after a "comprehensive" breakdown in industrial relations.
RMT has instructed all train operators and instructor operators not to book on for shifts after 21:00 on 23 March until 20:59 on 24 March.
And they've also been advised not to book on for shifts after 12:00 on 19 April until 11:59 on 20 April and again after 12:00 on 21 April until 11:59 on 22 April.
A ballot of nearly "400 train operators for both strike action and action short of a strike over a comprehensive breakdown in industrial relations combining a range of issues has recorded massive votes in favour," it said.
Some 85 per cent voted for strike action.
“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," said RMT general secretary Mick Cash.
"RMT will not sit back and allow individual members to be picked off by a vindictive and aggressive management who are continuing to drag their heels over addressing fundamental safety issues which leave staff in a vulnerable and exposed position," he added.
The result will now be considered by the union's executive.
However, the RMT added: "The union remains available for talks."
Pat Hansberry, operations director for London Underground, said: “It is disappointing that the RMT is once again threatening unnecessary strike action without seeking to resolve these local issues with us first. We urge the RMT to continue talks with us to resolve their issues rather than threatening to subject Londoners to another pointless strike.”