Talks aimed at averting a strike by London Underground workers in a row over the new all-night Tube are to be held at the conciliation service.
Members of the drivers union Aslef are due to walk out from the evening of July 8 for 24 hours.
Two other unions, the RMT and TSSA, are expected to announce next Tuesday that their members have also voted to go on strike.
An Acas spokesman said: "Acas will be convening talks on Tuesday in respect of the current dispute over pay and night Tube between London Underground, Aslef, RMT, TSSA and Unite."
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All night Tube services are due to start at weekends from mid September.