Workers at two rail companies are said to be solidly supporting strikes which are disrupting New Year's Eve train services.
Members of the Rail, Maritime and Transport union on South Western Railway (SWT) and CrossCountry walked out for 24 hours in separate disputes over the role of guards and working conditions.
The RMT claimed there were 141 unstaffed SWT stations which would become "crime hot spots and no-go areas for vulnerable and disabled passengers" if there are no guards.
RMT general secretary Mick Cash said: "No staff on trains, combined with no staff on the stations, will be a toxic mix for passengers at the locations we have identified which will increasingly become crime hot spots and no-go areas for vulnerable passengers, while drivers will also be alone and exposed.
"Our members are striking today on South Western Railway over these fundamental issues of public safety, security and access.
"There will be also be disadvantages for disabled and older passengers who require assistance because there will be no one there to help them on and off the train or provide assistance during their journey.
"These are yet another set of reasons why we will keep up the fight for a safe, secure and accessible railway with properly staffed stations and a guard on every train. These are the basic safety principles our members are striking for today on South Western Railway."
Andy Mellors, South Western Railway managing director, said: "The RMT executive knows we plan to keep a guard on all our trains to assist passengers. What we want to discuss with them is what happens when a guard is unavailable at short notice so that our passengers aren't left stranded.
"We have given them repeated reassurances that we will need more guards as we introduce new and longer trains. For the sake of our passengers and their members they need to stop scaremongering and start talking.
"We will do everything we can to keep our passengers moving during this unnecessary strike but passengers are warned to check before travelling and be prepared for queues if travelling back from the New Year's Eve fireworks."
The CrossCountry dispute is over rosters and Sunday working.
Mr Cash said: "Our members are standing up against rostering abuses and their action is rock solid across the franchise from Penzance to Aberdeen and the disruption to services is solely down to management's intransigence."
The union is planning more strikes in January against SWR, Southern, Merseyrail, Greater Anglia and Arriva Rail North in the bitter row over guards.