Jeremy Corbyn has announced he'd join a Southern rail picket line, saying he felt long-suffering commuters would support his position.
Speaking on Radio Four's Today programme, the Labour leader said he would stand in solidarity with those taking industrial action.
"Yes I would, because I think Southern rail have behaved in a terrible manner, and the government seems to be more interested in protecting Southern rail despite its appalling service and shortage of trains, overcrowding and all that goes with it, and continued allowing them to run the franchise on Southern," he said.
It comes as train drivers' union Aslef starts the first of three days of strike action on the network this week, over a dispute over the role of the guard.
Corbyn also said he wanted the franchise "brought back into the public ownership and public sector" as "we provide the rails, we provide the trains, and they make the profits from running them".
When asked whether his stance would be unpopular with commuters, whose journeys have been disrupted for months due to trouble on the network, Corbyn said: "On the contrary, I think many people who are trying to commute in from Brighton are utterly fed up with Southern rail and the way it's behaved."
Southern has advised people to avoid travelling during the industrial action unless it's essential, saying "no Southern services will operate today".
There are limited bus links from a small number of stations.
Union members also plan to walk out on 24, 25 and 26 January in the long-running dispute.
Angie Doll, Southern's passenger service director, said: "There will also be significant disruption and hardship on the days Aslef is not on strike because of their overtime ban, especially on Thursday when trains will be out of position because of the strikes on each day either side. We are deeply sorry for the unnecessary and unwarranted disruption this dispute is causing."
Mick Whelan, general secretary of Aslef, said: "We remain committed to a negotiated settlement, as was reached with ScotRail, but it is difficult to negotiate with people who are not prepared to be flexible. We still believe a deal can be done but we are, at the moment, a long way from that position."