The Rail, Maritime and Transport Workers union will ballot members over possible industrial action concerning the closure of ticket offices in London, resulting in the loss of 750 jobs.
RMT general secretary Bob Crow told radio station LBC that the union would serve notice of the ballot on the underground tomorrow.
The news follows the announcement by the Mayor of London Boris Johnson that the capital will have a 24-hour service on the underground at weekends from 2015.
Johnson said five lines will run round-the-clock services in the capital on Friday and Saturday nights.
They will be the Central, Piccadilly, Victoria and Jubilee lines, as well as sections of the Northern line.
But the underground's new plans involve the loss of 750 as many ticket offices will be closed.
Crow stressed he was in favour of the round-the-clock service, but questioned whether the service would remain safe.