The RMT has revealed its members will stage overnight walkouts on the Central and Victoria lines from 8.30pm on Fridays and Saturdays until June.
London Underground insists it's disappointed, and is calling for further talks.
The Union says it may broaden its strike to other lines if the transport operator fails to respond to its demands.
It’s also been staging action on the Northern, Piccadilly, and Jubilee lines in recent weeks.