This latest strike action threatens a fresh bout of travel chaos for commuters and tourists.
The drivers’ union Aslef accused LU of being “completely inflexible” over terms and conditions for the service, leaving it with “no other choice” than to press ahead with the walkout.
The union said the company should postpone the planned launch of the service on 12 September so that further negotiations could be held.
Aslef officer Finn Brennan said: “This leaves us with no other choice than to go ahead with strike action from 9.30pm on Wednesday (August 5).
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“We genuinely regret the disruption this will cause, but the blame for this must rest with the pig-headed determination of the mayor to insist on a September 12 launch of night Tube instead of allowing more time for a negotiated settlement to be reached.”
Other union members are due to strike from 6.30pm, meaning that disruption will start late in the afternoon as workers try to get home to beat the action.
London travel information
Transport for London said Tube services will stop running at 6.30pm on Wednesday, and urged people to complete journeys by this time and travel earlier if possible.
Tube services are expected to be “exceptionally busy” between 4.30pm and 6.30pm.
Staff on the bus network, DLR, London Overground, tram and TfL Rail services will not be on strike, but these services are expected to be much busier than usual.
There will be no Tube services all day on Thursday. Extra bus and river services will run, and all other public transport services and roads will be much busier than usual.