The Aslef unon says London Underground drivers will stage a second 24-hour strike in a dispute over night Tube plans, according to the BBC.
The walkout, set to start at 21:30 BST on 5 August, follows a strike that closed the entire network last week.
Conciliation service Acas has invited both sides to hold talks on Tuesday in a bid to avert the fresh strike.
The Unite union said it would join the planned action, BBC London’s transport correspondent Tom Edwards said.
Unions are unhappy about pay and shifts for the overnight service, which is due to start on 12 September.
An Acas spokesman said: “Acas has written to London Underground, Aslef, RMT, TSSA and Unite, inviting them to attend exploratory talks tomorrow morning.”
London Underground (LU) said it would attend the Acas-chaired talks.
The Rail, Maritime and Transport (RMT) union, the Transport Salaried Staffs Association (TSSA) and Unite union have yet to indicate their position on the talks or the August strike.
Members of the four trade unions were involved in the last strike, which began on Wednesday night.
The row is over a 2% average pay rise offer for LU members and workers’ terms and conditions linked to plans to introduce an all-night Tube service on the Jubilee and Victoria lines and and most of the Central, Northern and Piccadilly lines.
LU’s chief operating officer Steve Griffiths said earlier: “We will be at Acas tomorrow for further discussions to resolve this issue and trust the trade unions will be too.”
John Allan, chairman of the Federation of Small Businesses, said the prospect of a second Tube strike in less than a month was “disappointing news” and “another blow for businesses.”
“Many small companies proved their flexibility and resourcefulness last week, allowing their employees to work remotely, or hold meetings with clients online rather than in person.
“Nevertheless, there will be further damage to the economy and millions of pounds lost to businesses if this strike goes ahead,” he said.
Last week’s strike saw long delays and rush hour began earlier than normal as commuters tried to find alternative ways to get to and from work.
Millions of passengers walked, cycled, and took the bus and river services. Car booking firm Uber was criticised for its price surging practice as fares increased many times the normal price amid elevated demand.
London Mayor Boris Johnson condemned the strike as “unnecessary” and transport secretary Patrick McLoughlin urged workers to accept the offer made by London Underground.
The Tube strike was exacerbated by a 48-hour strike by First Great Western staff which affected some services between London, the West of England and Wales.