Hundreds of people attended a march in support of RMT strikers and climate justice, organisers said.
Supporters met at the Knights Templar pub in Temple Quay, Bristol, on Saturday and marched to Castle Park.
Salena Williams, of Bristol Climate Justice Coalition, said: "We need public transport run for people and the planet, not for profit."
Rail passengers across Britain are facing severely restricted services with about 30% of GWR trains running.
Downing Street said the unions should call off the strikes "as quickly as possible", but Mick Lynch, general secretary of the RMT, said Saturday's industrial action might not be the last.
Ms Williams said the demonstration - attended by about 400 people - was for all Bristolians "concerned about the climate".
"The government is cutting back on railways at a time when more people need to use public transport cheaply, easily and safely," she said.
"Getting rid of train guards and all ticket offices is a huge equality issue. We need a transport system accessible to all."
City councillor Amirah Cole said it was important for everyone to stick together.
She said: "If we accept inflation and no pay rise we are then working for little or nothing.
"We need cheaper and efficient trains back to cause less pollution and protect the climate," she added.
Speaking at the event, People's Assembly organiser Tom Whittaker quoted former RMT leader Bob Crow to say: "If you fight, you won't always win but if you don't fight, you'll always lose."
"This strike is a beacon of resistance, and public opinion is overwhelmingly in favour, because people can see if the RMT wins we all win," he added.
RMT regional organiser Brendan Kelly said National Rail, the Department of Transport and the government want to "cut jobs, cut pay and cut conditions".
However, he added "the reality on the railway of cutting those three things" is it "cuts safety".
Speaking on Wednesday, Dan Panes, spokesperson for Great Western Railway (GWR), said: "We need to sit down with the RMT and hash out a deal because that's the only way this is going to be solved."
GWR said it expected a later start to the timetable on Sunday with about 50% of trains running.
Mr Lynch has called on Transport Secretary Grant Shapps to engage in talks but Mr Shapps has accused the union of "damaging people's lives".
Writing on Twitter on Saturday, Mr Shapps said the rail industry must "move with the times" and "banish the outdated working practices that are holding it back".