The ongoing industrial dispute has been worsened by plans to close most ticket offices.
In a message to families whose summer holiday plans have been affected by the latest walk-out, the RMT senior assistant general secretary said “we need to stand together rather than fight each other".
Standing on a picket line outside Euston Station, Eddie Dempsey said: “What I’d say to them is, if they’re honest, people are going to find it difficult on a strike day.
"But everyone in this country is finding it hard when it’s not a strike day.
"And the reason for that is because we’ve got a Government that is presiding over a massive cost-of-living crisis, everybody’s wages have been falling, all of our public services are under-funded, we can see all of the services we rely on in the country in a state of managed decline, nothing’s getting better.”
