Rail users in South Yorkshire have been warned to expect delays today as the first of two days of industrial action gets underway.
The union RMT has organised two days of industrial action today and Thursday, which will affect Northern services between 7am and 7pm.
The industrial action is over the union's safety concerns as private train operators press ahead with plans for 'driver only' operations.
RMT General Secretary Mick Cash said: "These strikes are about safety. They are about putting the safety and security of the travelling public before the profits of private companies, profits that in the most part are shipped overseas to subsidise transport services in Europe and China. That is a national scandal.
"It is disgraceful that we have been unable to get serious and meaningful talks going in any of these five disputes and that points clearly to the dead-hand of the Government driving the faceless railway policy on purely ideological grounds and demanding that their contractors fall in line.
"RMT will not stand back while the guards, front-line staff when it comes to safety, security and access, are thrown off Britain's trains for political and financial reasons."