It’s led to more than 1,000 services being cancelled.
RMT General Secretary Mick Cash said;
“Our guards members on Southern Rail remain rock solid and absolutely determined in their action in defence of rail safety this morning.
“The union repeats it’s demand for Chris Grayling and his rail minister to get out of their bunker, stop the mud slinging and take up the offer from RMT for direct talks to sort out the worsening crisis on Britain’s biggest rail franchise.
“Tonight we will make another attempt to engage with Mr Grayling when he makes his big speech on breaking up and privatising Network Rail at the private Policy Exchange event.
“Instead of parading around the newsrooms with his lethal scheme to give outfits like Southern a chance to wreck rail infrastructure, as well as our train operations, the Transport Secretary should be in a room with the unions and GTR sorting out the current shambles. “