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13 July 2010, 11:28 | Updated: 16 July 2010, 10:34
The RMT union is to ballot all 10,000 of its members on the Underground for strike action.
The ballot, over job cuts to station and platform staff, will begin on Tuesday and close on August 11.
The union claims 800 posts are under threat and more than 140 ticket offices are being lined up for closure.
London Underground says there won't be compulsory redundancies.