Members of the Railway, Maritime and Transport Union (RMT) will refuse to appear for work on the Victoria and Central lines on Friday and Saturday.
Drivers belonging to the RMT will refuse to work from 20.30 on Friday until 8.30 on Saturday and from 20.30 on Saturday until 8.30 on Sunday.
RMT members and London Underground (LU) chiefs have been unable to resolve the dispute during recent discussions this week in the Acas conciliation service.
RMT said it was proposing to end the strike if LU agreed to a new set of “smart and realistic” proposals.
RMT Secretary General Mick Lynch said: “We are angry and disappointed that once again the proposal of our negotiators, which would pave the way for the cancellation of the current action, was rejected by the pipe leaders.
“Our proposal will address the central issue at the heart of this dispute – the balance of work and personal life.
“We are not retreating; the action continues, and if the government is going to lift some of Covid’s restrictions, LU must start serious negotiations. “
LU called the strikes unnecessary and advised passengers to check services before the trip.
A Transport for London spokesman said: “We are still open to talks with RMT, hoping the strike can be called off.
“We entered into negotiations in good faith this week, but there were no new proposals, and instead we were again offered to use our Night Tube services on a strictly volunteer basis, which was clearly unfeasible.
“As changes to our lists have been introduced, they have been a positive change for the organization and our staff, which has helped us keep London moving, become a fairer place to work and bring back the Night Tube.”
LU has updated travel advice in connection with the strikes, saying it expects good service on the Victoria line and at least two trains an hour on the center line.