Disability campaigners are to join a picket line being mounted by workers at Southern Railway during a fresh strike in a long-running row over changes to the role of conductors.
Members of the Rail, Maritime and Transport union will walk out for 48 hours from today, causing fresh travel chaos for hundreds of thousands of rail passengers.
More than two out of five trains will be cancelled, while there will be no service on some routes. Many trains will start late and finish early.
Campaigners from Disabled People Against Cuts will join an RMT picket line outside Victoria Station in London.
A spokesman said: "We believe that if a train runs driver-only operation to an unstaffed station with a passenger who is unable to exit the train unassisted, then an offence will be committed under the Equality Act 2010.
"After 30 years of commitment, effort and public expenditure to ensure that disabled people can travel by train, as by other modes, with confidence, we risk taking a significant retrograde step that will effectively deny people those hard-won rights. That is simply unacceptable."
RMT general secretary Mick Cash said: "The union supports the points raised by the disability campaigners, and the conclusion that the Govia Thameslink Railway plans represent an offence under the Equality Act 2010, as they will clearly put a disabled person at a substantial disadvantage.
"GTR, hoarding £100 million in profits and soaking up public funds, have ignored these points right from the off. That attitude is disgraceful."
Mr Cash said the guards' action was going ahead as planned. "RMT remains available for serious talks but GTR clearly have no interest in resolving the dispute and it is also clear that the Government are propping them up financially and politically," he said.
"Just a fraction of the £100 million the GTR parent company is hoarding in profits would be enough to keep a guard on the Southern trains, keep the trains safe and accessible and resolve the dispute. It is absolutely right to call for the Government to intervene and to hold those responsible for this continuing shambles to account."
Southern passenger services' director Alex Foulds said: "Passengers will be rightly dismayed that the RMT has chosen to disrupt services yet again.
"This two-day strike will achieve nothing. After many months of trying to reach agreement with the RMT, we are now moving forward with our plans for the benefit of customers and we urge the RMT to join us in putting passengers first.
"We have guaranteed all our on-board staff a job until the end of the franchise, with no reduction in salary. Our plans are safe, and will mean fewer cancelled trains. We are sorry that our passengers will once again suffer because of RMT intransigence, and we urge the union to work with us to find a sensible way forward."
Southern said it had put 119 trains back into its temporary weekday timetable, restoring the entire inner London metro service so that almost all London Bridge peak trains are now running, and tripling the number of trains operating on the West London Line.
The temporary timetable was introduced with 341 fewer trains on July 11 following "unprecedented" sickness levels among train crew.