The Transport Salaried Staffs' Association (TSSA) is the latest union to back the proposed Night Tube on the London Underground (LU). The move comes after tube drivers' union Aslef and the RMT both threw their support behind the much-delayed 24-hour weekend service.
The TSSA said 90% of its members accepted the latest pay and work conditions offer from Underground bosses in a referendum. The decision means the Night Tube is one step closer to being launched in the summer, after originally having a roll-out date of September 2015.
The service is now expected to launch on the Victoria and Jubilee lines in August, followed by the Central, Northern and Piccadilly Lines in September.
But Unite, which represents 600 of engineers and maintenance staff on the network, is yet to agree a deal with LU management.
LU is also currently in the process of training 180 part-time operators for the Night Tube.
A Transport for London spokesman previously told IBTimes UK: "No date has yet been agreed for the launch of the Night Tube, but we are working hard to deliver it for London as quickly as possible."
Meanwhile, a 24-hour-long strike will go ahead on the Piccadilly Line from 9pm (GMT) on 23 March.