Two senior Labour Party members are expected to take part in a demonstration against Theresa May's deal with the DUP on Saturday (July 1).
Shadow Home Secretary Diane Abbott and Shadow Chancellor John McDonnell will speak at the event, which has been arranged by The People's Assembly.
Momentum and the Labour Assembly Against Austerity are also joining the call for Jeremy Corbyn to become prime minister.
Demonstrators plan to march from the BBC's Broadcasting House to Parliament Square from 12pm.
Abbott, who is the co-chair of the Labour Assembly Against Austerity, said: "Saturday's demonstration will say 'no' to the Tory-DUP coalition of chaos and their continued commitment to austerity.
"Austerity has failed our economy, society and public services, making us all less safe. We need a positive alternative that puts people first."
The vice-chair of the assembly, MEP Lucy Anderson, added: "Theresa May failed to get the mandate she wanted for further austerity or her rigid and reckless hard Brexit.
"Rather than step aside, she has now entered a weak and wobbly coalition with the DUP that does not have support from the majority of people.
"Labour members from up and down the country will join Saturday's demonstration to back the alternative - Jeremy Corbyn for PM."