More than 20,000 members of the Rail, Maritime and Transport (RMT) union working for 14 rail companies went on strike on Saturday over pay and working conditions.
The RMT members also took industrial action on Thursday, and plan for another strike on July 29, as rail bosses announced more than 2,000 job cuts and the closure of 1,000 ticket offices in the country.
The National Rail warned the passengers of significant disruption, saying they should expect large areas of the rail network to have little or no services.
In a statement on Saturday, RMT general secretary Mick Lynch said: "Train companies invest little or nothing in our railways and make completely unjustifiable profits which they squirrel away in shareholder dividends and bosses pay packets."
"It is a scandal that the travelling public is being ripped off by greedy rail privateers while at the same time the government oversees a corrupt system and prolongs a rail dispute for political reasons," he added.
Source: Anadolu Agency