Night Tube strikes are set to take place on two Saturday nights next month, this will also be the first set of action taking place by the late night service.
Train drivers will walk out on the nights of April 8 and April 29.
More strikes could well occur due to a dispute over how the 24-hour service is staffed.
The Aslef union represents three quarters of the Night Tube drivers, it will declare its results of a strike ballot tomorrow afternoon.
After the the result the union’s executive committee will announce strike dates.
Aslef declined to comment before the announcement of the result.
Finn Brennan, Aslef’s London Underground district organiser, said: “The vast majority of Night Tube drivers took up the job because they saw it as a stepping stone to a full-time train driver’s job.”
“They believed LU’s assurances that they would have opportunities to progress, not to just spend year after year working every Friday and Saturday night.”