The mass rally will see RMT members, trades unionists and supporters from across the political landscape tell the government in no uncertain terms that ticket offices must be saved.
A consultation on the future of ticket offices which has received nearly 400,000 responses will close on September 1st and the union is encouraging everyone to take part.
Current plans will see up to 1000 ticket offices closed and 2,300 station staff jobs are in jeopardy.
RMT general secretary Mick Lynch said: "The public response to the government wanting to shut every ticket office in Britain has been very encouraging.
"People from different walks of life recognise the value of ticket offices and the station staff that support passengers on their journeys.
"Rail companies and their masters in government, do not care one jot about disabled people, vulnerable passengers and those travelling alone who welcome a human presence on our railways.
"These plans lock in age and disability discrimination and if they are carried out, it will mean many vulnerable passengers will not feel safe using the network.
"I urge everyone to take part in the consultation but our campaign will continue after the closing date of September 1st.
"We will be lobbying MPs, several of whom from across the political spectrum have been supportive of our campaign. And RMT will increase the pressure on the government to abandon its increasingly unpopular policy."