Anti-rail cut demonstrations are set to take place at Clapham Junction station tomorrow.
Members of the RMT and Battersea and Wandsworth TUC are railing against job losses in the sector.
They also argue that proposed changes suggested in the McNulty Rail Review will jeopardise passenger safety.
The McNulty review, publish in 2011, recommedned a number of ways the rail service could be run more cost efficiently.
Unions fear changes will see guards removed from trains and ticket offices closed.
Mick Cash, senior assistant general secretary of the RMT, said: "The plans to carve up our railways under the cloak of the McNulty Rail Review, would see the quality and safety of rails services out of Clapham Junction hammered into the ground.
"The public would pay ever-increasing fares to travel on unsafe and overcrowded trains on a faceless railway where profit is the only game in town."
The members will meet between 5.30pm and 6.30pm on Wednesday, and will give out information leaflets and talk to the public.
A Department for Transport spokesman said: "Franchising has been a force for good for our railways, delivering huge growth to an industry that was once in decline.
"Far from carving up our railways, we are investing record amounts to ensure they continue to grow.
"Network Rail will spend £38 billion over the next five years to expand and maintain the network."
At 7pm they will hold a public meeting at the Public and Commercial Services HQ building, 160 Falcon Road.